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


