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

int main()
{
  int a, b, c, d;

  cin  >> a >> b >> c >> d;

  while(a > 0 && c > 0){
    a -= d;
    c -= b;
  }

  if(c > 0){
    cout << "No" << endl;
  }
  else{
    cout << "Yes" << endl;
  }

  return 0; 
}
