#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
ll mod = 1000000007;

ll r(ll x, ll y) {
  if (y == 0) return 1;
  else if (y % 2 == 0) return r(x, y/2) * r(x, y/2) % mod;
  else return x * r(x, (y-1)/2) % mod * r(x, (y-1)/2) % mod;
}
  
int main() {
  int a, b, c,d;
  cin >> a >> b >> c >>d;
  int Ta = c / b;
  if (c%b!=0) {
    Ta++;
  }
  int Tb = a / d;
  if (a%d!=0) {
    Tb++;
  }
  if (Ta>Tb) {
    cout << "No" <<endl;
  }
  else {
    cout << "Yes" <<endl;
  }
} 
