#include <bits/stdc++.h>
using namespace std;

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