#include<bits/stdc++.h>
using namespace std;

int main(){
    constexpr long MOD = 1000000007;

    auto inv = [&MOD](auto i, auto j){
        long ret(j % MOD), n(MOD - 2);
        while(n){
            if(n & 1){
                ret *= i;
                ret %= MOD;
            }
            i *= i;
            i %= MOD;
            n >>= 1;
        }
        return ret;
    };

    long N, M, D, d;
    cin >> N >> M >> d >> D;

    D -= d;
    M -= d * (N - 1);
    if(M < 0)return 0 & puts("0");

    vector<long> P(M), Q(M), PP(M);

    P[0] = Q[0] = 1;
    for(long i = 1, j = 1, k = N; i < M; ++i)P[i] = j = inv(i, j * k++);
    for(long i = 1, j = 1, k = N; i * (D + 1) < M; ++i)Q[i * (D + 1)] = j = inv(i, (MOD - j) * --k);

    partial_sum(P.begin(), P.end(), PP.rbegin(), [&MOD](auto a, auto b){return (a + b) % MOD;});

    long ans(0);
    for(long i = 0; i < M; ++i)ans += Q[i] * PP[i] % MOD;
    cout << ans % MOD << endl;

    return 0;
}