#include <bits/stdc++.h>
#define rep(i,n) for ( int i = 0; i < (int)(n); i++)
using namespace std;
 
int main() {
  int a, b, c, d;
  cin >> a >> b >> c >> d;
  int count_a = a % d > 0 ? a / d + 1 : a / d;
  int count_c = c % b > 0 ? c / b + 1 : c / b;
  string result = count_a < count_c ? "No" : "Yes";
  cout << result << endl;
}
