#include<iostream>
#include<cstdio>
using namespace std;
const int N=2e5+10,p=1e9+7;
int fac[N],inv[N],h,w,a,b;
inline int C(int x,int y){
	return 1ll*fac[x]*inv[y]%p*inv[x-y]%p;
}
int main(){
	fac[0]=1;for (int i=1;i<N;++i) fac[i]=1ll*fac[i-1]*i%p;
	inv[0]=inv[1]=1;for (int i=2;i<N;++i) inv[i]=1ll*inv[p%i]*(p-p/i)%p;
	for (int i=2;i<N;++i) inv[i]=1ll*inv[i]*inv[i-1]%p;
	scanf("%d%d%d%d",&h,&w,&a,&b);
	int ans=C(h+w-2,h-1);
	for (int i=h-a,j=1;j<=b;++j) ans=(ans+p-1ll*C(i+j-2,j-1)*C(a-1+w-j,a-1)%p)%p;
	printf("%d",ans);
	return 0;
}