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

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