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

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