#include<bits/stdc++.h>
using namespace std;


int main(){
  int a,b,c,d;
  cin >> a >> b >> c >> d;
  while(a>0 && c>0){
    c=c-b;
    if(c<=0){
      cout << "Yes" << endl;
      return 0;
    }
    a=a-d;
    if(a<=0){
      cout << "No" << endl;
      return 0;
    }
  }
  return 0;
}
