#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1LL << 30;
int MOD = 1e9+7;
main(){
    ll H,W,N,K;
    cin >> H >> W >> N >> K;

    if(N == 1 || (H + W - 1) % N == K % N){
        cout << "YES" << endl;
    } else{
        cout << "NO" << endl;
    }
}