#include <bits/stdc++.h>
#define REP(i,n) for(int i=0;i<(n);++i)
using namespace std;
typedef long long LL;

int main() {
  int A, B, C, D;
  cin >> A >> B >> C >> D;
  int s = C / B + (C % B == 0 ? 0 : 1);
  int t = A / D + (A % D == 0 ? 0 : 1);
  cout << (s <= t ? "Yes" : "No") << endl;
}