#include <bits/stdc++.h>
#include <stdlib.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
typedef pair<ll,ll> llP;

int main() {
  int a,b,c,d;
  cin>>a>>b>>c>>d;
  int t=(b+c-1)/b;
  int A=(a+d-1)/d;
  if(t<=A) cout<<"Yes"<<endl;
  else cout<<"No"<<endl;
  return 0;
}
