#include <bits/stdc++.h>

using namespace std;

int main() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;

    while(1) {
        c -= b;
        if(c <= 0) {
            cout << "Yes" << endl;
            break;
        }

        a -= d;
        if(a <= 0) {
            cout << "No" << endl;
            break;
        }
    }

    return 0;
}
