#include<iostream>
#include<map>
#include<set>
#include<string>
#include<algorithm>
#include<cmath>
#include<vector>
#include<queue>
#include<stack>
#include<limits>
#include<sstream>      

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef int itn;

const int inf = numeric_limits<int>::max() /4;
const ll linf = numeric_limits<ll>::max() /4;
const ull ulinf = numeric_limits<ull>::max()/4;
const double pi = acos(-1);
const int dx[4]={1,0,-1,0};
const int dy[4]={0,1,0,-1};
const int dx8[8]={-1,0,1,-1,1,-1,0,1};
const int dy8[8]={-1,-1,-1,0,0,1,1,1};

#define p_queue(i) priority_queue<i> 
#define rp_queue(i) priority_queue<i, vector<i>, greater<i>> 
#define P(p) cout<<(p)<<endl
#define rep(i,m,n) for(int i = (m); i < (int)(n); i++)
#define mod(i) ((i)%(ll)(1e9 + 7))
#define divm(a,b) (mod(a * modpow((ll)b,(ll)(1e9+5))))
#define rsort(a,b,c) sort(a, b, greater<c>())
#define vsort(v) sort(v.begin(), v.end());
#define rvsort(v) sort(v.end(), v.begin());
#define ft first
#define sd second
#define pb push_back
#define it insert
#define sz(x) ((int)(x).size())
#define lb(a,n,k) (lower_bound(a,a+n,k) - a) 
#define vlb(a,k)  (lower_bound(a.begin(),a.end(),k) - a.begin())
#define ub(a,n,k) (upper_bound(a,a+n,k) - a) 
#define vub(a,k)  (upper_bound(a.begin(),a.end(),k) - a.begin())
#define YES cout<<"YES"<< endl
#define NO cout<<"NO"<<endl
#define Yes cout<<"Yes"<<endl
#define No cout<<"No"<<endl  
#define yes cout<<"yes"<<endl
#define no cout<<"no"<<endl
#define ret return

ll modpow(ll i,ll j){ ll tmp=1; while(j){ if(j%2)tmp=mod(tmp*i);i=mod(i*i);j/=2;}return tmp;}
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

vector<string> split(const string &str, char sep){
    vector<string> v;
    stringstream ss(str);
    string buffer;
    while( getline(ss, buffer, sep) ) {
        v.push_back(buffer);
    }
    return v;
}

//ll ncr[100][100];
//ll nCr(int n, int r){if(n==r) ret ncr[n][r] = 1;if(r==0) ret ncr[n][r] = 1; if(r==1) ret ncr[n][r] = n;if(ncr[n][r]) ret ncr[n][r]; ret ncr[n][r] = nCr(n-1,r) + nCr(n-1,r-1);}

//ll npr[100][100]={};
//ll nPr(int n,int r){if(npr[n][r])ret npr[n][r];if(r==0)ret npr[n][r] = 1;if(r==1)ret npr[n][r] = n;ret npr[n][r] = n * nPr(n-1,r-1);}

//ll nHr(int n,int r){ret nCr(n+r-1,r);}

///////////////////////////////////////////////////////////////////////////


template <typename Int, int N>
struct mod_CPH {
    array<Int, N + 1> fc, ifc;

    mod_CPH() {
        fc[0] = 1;
        for (int i = 1; i <= N; i++) fc[i] = mod(fc[i - 1] * i);
        ifc[N] = modpow(fc[N],1e9+5);
        for (int i = N - 1; i >= 0; i--) ifc[i] = mod(ifc[i + 1] * (i + 1));
    }

    Int nPr(Int n, Int r) {
        if (r < 0 || n < r)return 0;
        return mod(fc[n] * ifc[n - r]);
    }

    Int nCr(Int n, Int r) {
        if (n < 0 || r < 0 || n < r) return 0;
        return mod(mod(fc[n] * ifc[r])*ifc[n - r]);
    }

    Int nHr(Int n, Int r) {
        if (n < 0 || r < 0) return 0;
        return r == 0 ? 1 : nCr(n + r - 1, r);
    }
};


mod_CPH<ll,2000000> mc;

int main(){
    ll h,w,a,b;
    cin >> h >> w >> a >> b ;
	h--;
	w--;
	
	ll ans = 0;

	while(b <= w){
        ans += mod((mc.nCr(b+h-a,min(b,h-a))) * (mc.nCr(w-b+a-1,min(w-b,a-1))));
        ans = mod(ans);
        b++;
	}
	P(ans);
	
	return  0;
}

Measured memory_bytes: 31616