#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
int main() {
  ll l, r, m, k, n = 0;
  cin >> l >> r >> m >> k;
  r *= k;
  l *= k;
  if(r - l >= m || k == 0) {
    cout << "Yes\n";
  } else if(r != l && r % m <= l % m) {
    cout << "Yes\n";
  } else if(r == l && r % m == 0){
    cout << "Yes\n";
  }else{
    cout << "No\n";
  }
  return 0;
}