#include<iostream>
using namespace std;
const long M=1e9+7;
long pow(long a,int b){return b?b%2?pow(a*a%M,b/2)*a%M:pow(a*a%M,b/2):1;}
long memo[1<<18];
int main()
{
	*memo=1;
	for(int i=1;i<1<<18;i++)memo[i]=memo[i-1]*i%M;
	long h,w,a,b;cin>>h>>w>>a>>b;
	long ans=0,now;
	for(int i=b;i<w;i++)
	{
		now=memo[h-a-1+i]%M*pow(memo[h-a-1],M-2)%M*pow(memo[i],M-2)%M;
		now=now*memo[a+w-i-2]%M*pow(memo[a-1],M-2)%M*pow(memo[w-i-1],M-2)%M;
		ans=(ans+now)%M;
	}
	cout<<ans<<endl;
}