#include <iostream>
using namespace std;

typedef long long ll;

ll H, W, N, K;

void Solve() {
    if ((H + W - 2) % N == K - 1) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}

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

    Solve();

    return 0;
}