#include <bits/stdc++.h> #include <atcoder/all> using namespace std; using namespace atcoder; using ll = long long; using ld = long double; int h, w, n, k, x; int main() { cin >> h >> w >> n >> k; x = (h * w - 1) % n; cout << (x == k - 1 ? "YES": "NO") << endl; return 0; }