#include <bits/stdc++.h>
using namespace std;
 
int main(){
    int A, B, C, D; cin >> A >> B >> C >> D;

    while(A>0){
        C -= B;
        if(C<=0){
            cout << "Yes" << endl;
            return 0;
        }

        A -= D;

    }

    cout << "No" << endl;

}