#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=2e5+10,P=1e9+7;
int qpow(int a,int b){int ans=1;for(;b;b>>=1,a=a*a%P)if(b&1)ans=ans*a%P;return ans;}
int fac[N];
int C(int n,int m){return fac[n]*qpow(fac[m],P-2)%P*qpow(fac[n-m],P-2)%P;}
signed main()
{
	int n,m,a,b;cin>>n>>m>>a>>b;int ans=0;
	fac[0]=1;for(int i=1;i<=N-10;i++)fac[i]=fac[i-1]*i%P;
	for(int i=1;i<=m-b;i++)
	{
		int h=i,w=a;if(h<w)swap(h,w);
		int h1=n-a,h2=m-i+1;if(h1<h2)swap(h1,h2);
		ans=(ans+C(h+w-2,w-1)*C(h1+h2-2,h2-1))%P;
	}
	cout<<ans;
	return 0;
}