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

const int64_t MOD = 1e9 + 7;

int main() {
  int64_t H, W, N, K;
  cin >> H >> W >> N >> K;
  if ((H * W % N - 1) % N + 1 == K) cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}