#include <iostream>
using namespace std;

int main (void) {
    long long int H, W, N, K, ans = 0;
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> H >> W >> N >> K;

    ans = (H + W - 1) % N;
    if (ans == 0) ans += N;
    if (ans == K) cout << "YES\n";
    else cout << "NO\n";

    return 0;
}