#include<bits/stdc++.h>
using namespace std;
const int mod=1e9+7;
typedef long long ll;
const int N=200000;
ll fac[N+5],inv[N+5];
int h,w,a,b;
ll fast_pow(int a,int b)
{
	ll res=1,tmp=a;
	for(;b;tmp=tmp*tmp%mod,b>>=1)
		if(b&1) res=res*tmp%mod;
	return res;
}
ll work(int n,int m)
{
	return fac[n]*inv[m]%mod*inv[n-m]%mod;
}
int main()
{
	fac[0]=1;for(int i=1;i<=N;++i) fac[i]=fac[i-1]*i%mod;
	
	inv[N]=fast_pow(fac[N],mod-2);
	for(int i=N-1;i>=0;--i)
	inv[i]=(i+1)*inv[i+1]%mod;
	scanf("%d%d%d%d",&h,&w,&a,&b);
	a=h-a;b++;
	ll ans=0;
	for(int i=1;i<=a;++i) ans=(ans+work(b+i-3,b-2)*work(h-i+w-b,h-i)%mod)%mod;
	cout<<ans;
}