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

int main(){
  long long h, w, n, k;
  cin >> h >> w >> n >> k;
  long long out;
  if((h + w - 1) % n == k){
    cout << "YES" << endl;
  }else if((h + w - 1) % n == 0 && n == k){
    cout << "YES" << endl;
  }else{
    cout << "NO" << endl;
  }
}