#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
int main(void){
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    if((c+b-1)/b<=(a+d-1)/d) cout << "Yes" << endl;
    else cout << "No" << endl;
}
