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

int main() {
  int a,b,c,d; cin>>a>>b>>c>>d;
  bool ok=false;
  while (1) {
    a-=d;
    if (a<=0) {
      ok=true;
      break;
    }
    c-=b;
    if (c<=0) {
      ok=false;
      break;
    }
  }
  if (ok) cout<<"Yes"<<endl;
  else cout<<"No"<<endl;
}
