#include<stdio.h>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<set>
#include<cassert>
#include<map>
#include<string>
#include<iostream>
#include<ext/pb_ds/priority_queue.hpp>
#include<queue>
#include<stack>
#include<bitset>
#include<tr1/unordered_map>
#include<tr1/unordered_set>
#define pb push_back
#define all(a) a.begin(),a.end()
#define pointtype double
#define pointtype_INT 0
using namespace std;
using namespace tr1;
typedef long long LL;
typedef pair<int,int>pii;
typedef unsigned uint;
typedef unsigned long long uLL;
const double pi=acos(-1);
template<class T>
void Read(T &x){
	char c;
	bool f(0);
	while(c=getchar(),c!=EOF){
		if(c=='-')
			f=1;
		else if(c>='0'&&c<='9'){
			x=c-'0';
			while(c=getchar(),c>='0'&&c<='9')
				x=x*10+c-'0';
			ungetc(c,stdin);
			if(f)
				x=-x;
			return;
		}
	}
}
struct point{
	pointtype x,y;
	inline point(){
	}
	inline point(pointtype x,pointtype y=0):x(x),y(y){
	}
	inline point operator+(const point &a)const{
		return point(x+a.x,y+a.y);
	}
	inline point operator+=(const point &a){
		return *this=*this+a;
	}
	inline point operator-(const point &a)const{
		return point(x-a.x,y-a.y);
	}
	inline point operator-=(const point &a){
		return *this=*this-a;
	}
	inline bool operator<(const point &b)const{
		if(x==b.x)
			return y<b.y;
		return x<b.x;
	}
	inline bool operator==(const point &b)const{
		return x==b.x&&y==b.y;
	}
	#if pointtype_INT==1
		inline point operator*(const point &a)const{
			return point(1ll*x*a.x-1ll*y*a.y,1ll*x*a.y+1ll*y*a.x);
		}
		inline friend LL cross(const point &a,const point &b){
			return 1ll*a.x*b.y-1ll*a.y*b.x;
		}
		inline friend LL dot(const point &a,const point &b){
			return 1ll*a.x*b.x+1ll*a.y*b.y;
		}
	#else
		inline point operator*(const point &a)const{
			return point(x*a.x-y*a.y,x*a.y+y*a.x);
		}
		inline friend pointtype cross(const point &a,const point &b){
			return a.x*b.y-a.y*b.x;
		}
		inline friend pointtype dot(const point &a,const point &b){
			return a.x*b.x+a.y*b.y;
		}
	#endif
};
template<class T,class T2>
struct hashnode{
	T val;
	T2 v;
	hashnode *next;
};
template<class T,class T2>
inline int& addhash(int u,const T &val,T2 *&ecnt,T2 **adj){
	T2 *p=++ecnt;
	p->val=val;
	p->v=0;
	p->next=adj[u];
	adj[u]=p;
	return p->v;
}
template<class T,class T2,int MOD,int ss>
class hash_table{
	hashnode<T,T2>*adj[MOD],edge[ss+10],*ecnt;
	int sz;
	public:
	inline int Get_val(int x){
		return x%MOD;
	}
	#if pointtype_INT==1
		inline int Get_val(point x){
			return (x.x*998244353ll+x.y)%MOD;
		}
	#endif
	inline hash_table():ecnt(edge),sz(0){
		for(int i=0;i<MOD;i++)
			adj[i]=0;
	}
	inline int size(){
		return sz;
	}
	inline hashnode<T,T2>* hash(const T &x){
		int t=Get_val(x);
		for(hashnode<T,T2> *p=adj[t];p;p=p->next)
			if(p->val==x)
				return p;
		return 0;
	}
	inline int &operator[](const T &x){
		hashnode<T,T2> *p=hash(x);
		if(p)
			return p->v;
		return ++sz,addhash(Get_val(x)%MOD,x,ecnt,adj);
	}
	inline bool count(const T &x){
		return hash(x);
	}
	inline void clear(){
		ecnt=edge;
		int t=MOD>>2<<2,i;
		for(i=0;i<t;i+=4){
			adj[i]=0;
			adj[i+1]=0;
			adj[i+2]=0;
			adj[i+3]=0;
		}
		for(;i<MOD;i++)
			adj[i]=0;
		sz=0;
	}
};
template<int sz,int MOD>
struct Matrix{
	int a[sz][sz];
	inline Matrix(){
		memset(a,0,sizeof a);
	}
	inline Matrix(int){
		memset(a,0,sizeof a);
		for(int i=0;i<sz;i++)
			a[i][i]=1;
	}
	inline void clear(){
		memset(a,0,sizeof a);
	}
	inline Matrix operator *(const Matrix &b)const{
		static Matrix c;
		c.clear();
		int i,j,k;
		for(i=0;i<sz;i++)
			for(j=0;j<sz;j++)
				if(a[i][j])
					for(k=0;k<sz;k++)
						c.a[i][k]=(c.a[i][k]+1ll*a[i][j]*b.a[j][k])%MOD;
		return c;
	}
	inline Matrix &operator *=(const Matrix &b){
		return *this=*this*b;
	}
	friend Matrix quick_pow(Matrix a,int b){
		Matrix ret(1);
		while(b){
			if(b&1)
				ret*=a;
			a*=a;
			b>>=1;
		}
		return ret;
	}
};
struct cpx{
	double r,i;
	inline cpx(){
	}
	inline cpx(double r,double i=0):r(r),i(i){
	}
	inline cpx operator+(const cpx &a)const{
		return cpx(r+a.r,i+a.i);
	}
	inline cpx operator-(const cpx &a)const{
		return cpx(r-a.r,i-a.i);
	}
	inline cpx operator*(const cpx &a)const{
		return cpx(r*a.r-i*a.i,r*a.i+i*a.r);
	}
	inline cpx operator/(const double &a)const{
		return cpx(r/a,i/a);
	}
	inline cpx operator/(const cpx&a)const{
		return *this*cpx(a.r,-a.i)/(a.r*a.r+a.i*a.i);
	}
	inline cpx operator+=(const cpx &a){
		return *this=*this+a;
	}
	inline cpx operator-=(const cpx &a){
		return *this=*this-a;
	}
	inline cpx operator*=(const cpx &a){
		return *this=*this*a;
	}
	inline cpx operator/=(const cpx &a){
		return *this=*this/a;
	}
	inline cpx conj(){
		return cpx(r,-i);
	}
};
template<class T,int len>
struct polynomial{
	T a[len];
	inline void clear(){
		int t=len>>2<<2,i;
		for(i=0;i<t;i+=4){
			a[i]=0;
			a[i+1]=0;
			a[i+2]=0;
			a[i+3]=0;
		}
		for(;i<len;i++)
			a[i]=0;
	}
	inline polynomial operator+(const polynomial &b)const{
		static polynomial c;
		int t=len>>2<<2,i;
		for(i=0;i<t;i+=4){
			c.a[i]=a[i]+b.a[i];
			c.a[i+1]=a[i+1]+b.a[i+1];
			c.a[i+2]=a[i+2]+b.a[i+2];
			c.a[i+3]=a[i+3]+b.a[i+3];
		}
		for(;i<len;i++)
			c.a[i]=a[i]+b.a[i];
		return c;
	}
	inline polynomial operator+=(const polynomial &b){
		return *this=*this+b;
	}
	inline polynomial operator-(const polynomial &b)const{
		static polynomial c;
		int t=len>>2<<2,i;
		for(i=0;i<t;i+=4){
			c.a[i]=a[i]-b.a[i];
			c.a[i+1]=a[i+1]-b.a[i+1];
			c.a[i+2]=a[i+2]-b.a[i+2];
			c.a[i+3]=a[i+3]-b.a[i+3];
		}
		for(;i<len;i++)
			c.a[i]=a[i]-b.a[i];
		return c;
	}
	inline polynomial operator-=(const polynomial &b){
		return *this=*this-b;
	}
	inline polynomial operator*(const polynomial &b){
		static polynomial ret;
		ret.clear();
		for(int i=0;i<len;i++)
			for(int j=0;j<=i;j++)
				ret.a[i]+=a[j]*b.a[i-j];
		return ret;
	}
	inline void Antiderivative(int c){
		int i;
		for(i=len-1;i;i--)
			a[i]=a[i-1]/i;
		a[0]=c;
	}
	inline T Get_val(T c){
		T ret(a[0]);
		for(int i=1;i<len;i++){
			ret+=c*a[i];
			c*=c;
		}
		return ret;
	}
};
void fft(cpx *a,int N,int f){
	int i,j=0,k,t;
	for(i=1;i<N-1;i++){
		for(t=N;j^=t>>=1,~j&t;);
		if(i<j)
			swap(a[i],a[j]);
	}
	for(i=1;i<N;i<<=1){
		cpx wn(cos(pi/i),f*sin(pi/i));
		t=i<<1;
		for(j=0;j<N;j+=t){
			cpx w(1,0);
			for(k=0;k<i;k++,w*=wn){
				cpx x(a[j+k]),y(w*a[j+k+i]);
				a[j+k]=x+y,a[j+k+i]=x-y;
			}
		}
	}
	if(f==-1)
		for(i=0;i<N;i++)
			a[i].r/=N;
}
void mul(cpx *a,cpx *b,cpx *c,cpx *t,int N){
	int i,j;
	for(i=0;i<N;i++)
		t[i]=cpx(a[i].r,b[i].r);
	fft(t,N,1);
	for(i=0;i<N;i++){
		j=(N-i)&(N-1);
		c[i]=(t[i]*t[i]-(t[j]*t[j]).conj())*cpx(0,-0.25);
	}
	fft(c,N,-1);
	// c refer t
	//a[i]=(c[i]+c[k-i])/2
	//b[i]=-i(c[i]-c[k-i])/2
	//a[i]*b[i]=(c[i]*c[i]-c[k-i]*c[k-i])*((-i)/4)
}
namespace mypq{
	template<class T,class Container=std::vector<T>,class cmp=std::less<typename Container::value_type> >
	struct priority_queue{
		std::priority_queue<T,Container,cmp>ins,del;
		inline void push(T a){
			ins.push(a);
		}
		inline void erase(T a){
			del.push(a);
		}
		inline void pop(){
			while(!del.empty()&&ins.top()==del.top())
				ins.pop(),del.pop();
			ins.pop();
		}
		inline T top(){
			while(!del.empty()&&ins.top()==del.top())
				ins.pop(),del.pop();
			return ins.top();
		}
		inline T second_top(){
			T tmp=top(),ret;
			pop();
			ret=top();
			push(tmp);
			return ret;
		}
		inline void clear(){
			while(!ins.empty())
				ins.pop();
			while(!del.empty())
				del.pop();
		}
		inline int size(){
			return ins.size()-del.size();
		}
		inline bool empty(){
			return !size();
		}
	};
}
void exgcd(long long a,long long b,long long &d,long long &x,long long &y){
    if(!b){
        d=a;
        x=1;
        y=0;
        return;
    }
    exgcd(b,a%b,d,y,x);
    y-=a/b*x;
}
//template
#define MAXN 100000
#define MOD 1000000007
int n,m,a,b,fac[MAXN*2+10],inv[MAXN*2+10],ans;

void prepare(){
	int i;
	fac[0]=fac[1]=inv[1]=inv[0]=1;
	for(i=2;i<=n+m;i++){
		fac[i]=1ll*i*fac[i-1]%MOD;
		inv[i]=1ll*(MOD-MOD/i)*inv[MOD%i]%MOD;
	}
	for(i=2;i<=n+m;i++)
		inv[i]=1ll*inv[i]*inv[i-1]%MOD;
}
int C(int n,int m){
	return 1ll*fac[n]*inv[m]%MOD*inv[n-m]%MOD;
}
int main()
{
	Read(n),Read(m),Read(a),Read(b);
	prepare();
	ans=C(n+m-2,n-1);
	if(a==n){
		puts("0");
		return 0;
	}
	for(int i=1;i<=b;i++)
		ans=(ans-1ll*C(n-a+i-2,n-a-1)*C(a-1+m-i,a-1)%MOD+MOD)%MOD;
	cout<<ans<<endl;
}