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

template<typename T>
void fin(T a){
  cout<<a<<endl;
  exit(0);
}

signed main(){
  int a,b,c,d;cin>>a>>b>>c>>d;
  while(1){
    c-=b;if(c<=0)fin("Yes");
    a-=d;if(a<=0)fin("No");
  }
}
