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

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int c;
  cin >> c;
  ll l = 0, r = 4'000;
  constexpr ll mul = 1'000'000'000'000'000;
  while (r - l > 1) {
    ll mid = (l + r) / 2;
    ll t = mid * mid * mid * mid * mid + mid * (mul / 1'000);
    // cerr << format("{}: {} {}", mid, t, c * mul) << '\n';
    (t <= c * mul ? l : r) = mid;
  }
  cout << format("{}.{:0>3}", l / 1'000, l % 1'000) << '\n';
  return 0;
}