#include <bits/stdc++.h>

using namespace std;

struct Initializer {
  Initializer() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15);
  }
} initializer;

int main() {
  int64_t h, w, n, k;
  cin >> h >> w >> n >> k;
  cout << ((h + w - 2) % n == k - 1 ? "YES" : "NO") << endl;
}