#include <iostream>
#include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
#define rep(i,n) for(int i = 0; i < ((int)(n)); i++)   // 0-indexed昇順

int main() {
    int A, B, C, D;
    cin >> A >> B >> C >> D;
    while (1) {
        C -= B;
        if (C <= 0) {
            cout << "Yes" << endl;
            return 0;
        }
        A -= D;
        if (A <= 0) {
            cout << "No" << endl;
            return 0;
        }
    }
}
