#include <iostream>
using namespace std;
int main()
{
  int a,b,c,d;
  cin>>a>>b>>c>>d;
  for(int i=0; ;i++){
    if(i%2==0)c-=b;
    else a-=d;
    if(a<=0){cout<<"No"<<endl; break;}
    else if(c<=0){cout<<"Yes"<<endl; break;}
  }
  
  return 0;
}