#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 -= b;
    a -= d;
  }
  if(c<=0) cout << "Yes" << endl;
  else  cout << "No" << endl;

  return 0;
}
