#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
#include <cmath>
using namespace std;
using ll = long long;

ll h, w, n, k;

int main()
{
  cin >> h >> w >> n >> k;
  if ((h + w - 2) % n == k - 1)
    cout << "YES";
  else
    cout << "NO";
  cout << endl;
  return 0;
}