#include <bits/stdc++.h>
#define ll long long int
#define MOD 1000000007
#define INF 1e18

using namespace std;

int main(void){
  ll a, b, c, d;
  cin >> a >> b >> c >> d;
  
  if ((c + b - 1) / b <= (a + d - 1)/d)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
    

  return 0;
}
