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

int main(){
    long long H, W, N, K;
    cin >> H >> W >> N >> K;
    if ((H+W-1)%N==K%N) cout << "YES" << endl;
    else cout << "NO" << endl;
    return 0;
}