#include <iostream>
using namespace std;
using ll = long long;
void ins() {}
template<class T,class... Rest>void ins(T& v,Rest&... rest){cin>>v;ins(rest...);}

const string yes = "Yes", no = "No";
int main() {
  ll L, R, M, K;
  ins(L, R, M, K);


  if (M * (R / M) > L) {
    cout << yes << "\n";
    return 0;
  }
  if (K == 0 || L == 0) {
    cout << yes << "\n";
    return 0;
  }

  cout << (M * (R * K / M) >= L * K ? yes : no) << "\n";

  return 0;
}