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

int main(){
    constexpr long MOD = 1000000007;

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

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

    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;
    };

    vector<long> invmod(M);
    invmod[1] = 1;
    for(long i = 2; i < M; ++i){
        auto k = invmod[i >> 1];
        invmod[i] = (k + (k & 1) * MOD) >> 1;
        ++i;
        invmod[i] = inv(i, 1);
    }

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

    partial_sum(P.begin(), P.end(), PP.rbegin());
    cout << inner_product(Q.begin(), Q.end(), PP.begin(), 0L, plus<>(), [&MOD](auto a, auto b){return (a * (b % MOD)) % MOD;}) % MOD << endl;

    return 0;
}