#include <iostream>
using namespace std;

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

    while (1) {
        if (!H || !W) break;

        if (H >= W) {
            H--;
        } else {
            W--;
        }
        ans++;
        if (ans > K) ans = 1;
    }
    if (ans == K) cout << "YES\n";
    else cout << "NO\n";

    return 0;
}