#include <iostream>
using namespace std;

int main() {
    int a, b, c, d; cin >> a >> b >> c >> d;
    while (1) {
        c -= b;
        if (c <= 0) break; 
        a -= d;
        if (a <= 0) break;
    }
    if (a <= 0) cout << "No" << endl;
    else cout << "Yes" << endl;
}