#include<bits/stdc++.h>

using namespace std;

typedef long long int ll;

int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(0);cout.tie(0);

  ll a, b, c, d;
  cin >> a >> b >> c >> d;

  ll p = a / d, q = c / b;
  if(a % d != 0) p++;
  if(c % b != 0) q++;
  if(q <= p) cout << "Yes" << endl;
  else cout << "No" << endl;
}
