#include "bits/stdc++.h"
using namespace std;
#define watch(x) cout << (#x) << " is " << (x) << endl

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  int h1,s1,h2,s2;
  cin>>h1>>s1>>h2>>s2;

  while(h2>0 && h1>0){
     h2-=s1;
     if(h2<=0){
       cout<<"Yes"<<endl;
       return 0;
     }
     h1-=s2;   
     if(h1<=0){
       cout<<"No"<<endl;
       return 0;
     }

  }
  
  

  
     
  return 0;
}
