#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
const long long INF = 1LL << 60; 

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