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

int main() {
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    bool ans;
    while(a > 0 && c > 0){
        c -= b;
        if(c <= 0) ans = true;
        else{
            a -= d;
            if(a <= 0) ans = false;
        }
    }

    if(ans) cout << "Yes" << endl;
    else cout << "No" << endl;
}