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

int main()
{
  int a, b, c, d;
  int a_num, c_num;

  cin >> a >> b >> c >> d;
  a_num = (c + b - 1) / b;
  c_num = (a + d - 1) / d;

  string ans;
  if(a_num >= c_num){
    ans = "Yes";
  } else {
    ans = "No";
  }

  cout << ans << endl;
}