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