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

int main() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    
    for (;;) {
        c -= b;
        if (c <= 0) {
            puts("Yes");
            return 0;
        }
        a -= d;
        if (a <= 0) {
            puts("No");
            return 0;
        }
    }
}