#include <bits/stdc++.h>
using namespace std;
int main()
{
   ios::sync_with_stdio(false);
   cin.tie(0);
   cout.tie(0);
    
  int a,b,c,d;
  cin>>a>>b>>c>>d;
  
  int x1 = c/b  , x2 = a/d;
  
  c = c-x1*b;
  a = a-x2*d;
  
  if(a==1)
  cout<<"Yes"<<endl;
  else
  cout<<"No"<<endl;
   
   return 0;
}
