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

int main(){
    ll H, W, N, K;
    cin >> H >> W >> N >> K;

    ll masu = H * W;
    ll last = (masu - 1) % N + 1;

    cout << ((last == K) ? "YES" : "NO") << endl;
    return 0;
}