#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  ll h, w, n, k;
  cin >> h >> w >> n >> k;
  cout << ((h + w - 2) % n == k - 1 ? "YES" : "NO") << '\n';
  return 0;
}