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

typedef long long ll;

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