// includes #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include // macros #define ll long long int #define pb emplace_back #define mk make_pair #define pq priority_queue #define FOR(i, a, b) for(int i=(a);i<(b);++i) #define rep(i, n) FOR(i, 0, n) #define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--) #define all(x) (x).begin(),(x).end() #define sz(x) ((int)(x).size()) #define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end()) using namespace std; // types typedef pair P; typedef pair Pl; typedef pair Pll; typedef pair Pd; // constants const int inf = 1e9; const ll linf = 1LL << 50; const double EPS = 1e-10; const int mod = 1e9 + 7; // solve template bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;} template bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;} ll fac[600001], inv[600001]; template T power(T a, T n, T mod) { T res = 1; T tmp = n; T curr = a; while(tmp){ if(tmp % 2 == 1){ res = (T)((ll)res * curr % mod); } curr = (T)((ll)curr * curr % mod); tmp >>= 1; } return res; } ll comb(ll n, ll k){ ll res = 1; res = res * fac[n] % mod; res = res * inv[k] % mod; res = res * inv[n-k] % mod; return res; } ll h(ll n, ll k){ return comb(n + k - 1, n); } int main(int argc, char const* argv[]) { ios_base::sync_with_stdio(false); cin.tie(0); ll n, m, d1, d2; cin >> n >> m >> d1 >> d2; fac[0] = 1; for(int i = 1; i < 600001; i++)fac[i] = i * fac[i-1] % mod; inv[600000] = power(fac[600000], mod - 2, mod); for(int i = 599999; i >= 0; i--)inv[i] = (i + 1) * inv[i+1] % mod; ll res = 0; for(int p = 0; p < n; p++){ ll M = m - (n - 1) * d1 - 1 - p * (d2 - d1 + 1); if(M < 0)continue; ll tmp = comb(n - 1, p) * h(M, n + 1); if(p % 2 == 0)res = (res + tmp) % mod; else res = (res - tmp) % mod; if(res < 0)res += mod; } cout << res << endl; return 0; }