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

#define int long long

signed main(){
	ios_base::sync_with_stdio(false);
	int H,W,N,K;
	cin >> H >> W >> N >> K;
	if( (H+W-2) % N == K-1 ) cout << "YES" << endl;
	else cout << "NO" << endl;
	
}