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

typedef long long ll;

const string msg[] = { "YES", "NO" };

signed main(){
  ll H, W, N, K; cin >> H >> W >> N >> K;
  ll turn = H * W - 1;
  cout << msg[ N % turn == K - 1 ] << endl;
  return 0;
}