#include<stdio.h>
int main(void){
  char *s="python3 -c\""
"class Factorial:\n"
"    def __init__(self,n,mod):\n"
"        self.f=[1]\n"
"        for i in range(1,n+1):\n"
"            self.f.append(self.f[-1]*i%mod)\n"
"        self.i=[pow(self.f[-1],mod-2,mod)]\n"
"        for i in range(1,n+1)[::-1]:\n"
"            self.i.append(self.i[-1]*i%mod)\n"
"        self.i.reverse()\n"
"    def factorial(self,i):\n"
"        return self.f[i]\n"
"    def ifactorial(self,i):\n"
"        return self.i[i]\n"
"    def comb(self,n,k):\n"
"        return self.f[n]*self.i[n-k]%mod*self.i[k]%mod\n"
"mod=10**9+7\n"
"h,w,a,b=map(int,input().split())\n"
"f=Factorial(h+w,mod)\n"
"ans=0\n"
"for i in range(b,w):\n"
"    ans=(ans+f.comb(h-a-1+i,i)*f.comb(a-1+w-i-1,w-i-1))%mod\n"
"print(ans)\n"
"\"";
  system(s);
  return 0;
}            