// verification-helper: PROBLEM https://yukicoder.me/problems/4117

#include<bits/stdc++.h>
using namespace std;

#define call_from_test
struct BoolPrinter{
  const string a,b;
  BoolPrinter(string a_,string b_):a(a_),b(b_){}
  string operator[](int k){return k?a:b;}
};
BoolPrinter yesno("yes","no");
BoolPrinter YesNo("Yes","No");
BoolPrinter YESNO("YES","NO");

#undef call_from_test

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);

  long long l,r,m,k;
  cin>>l>>r>>m>>k;

  long long x=l*k,y=r*k;
  cout<<YesNo[x<=y/m*m]<<endl;
  return 0;
}