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

int main() {
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	
	ll C;
	cin >> C;
	
	ll A = 1;
	rep(itr, 0, 12) A *= 10;
	ll B = A * 1000;
	
	ll ok = 0, ng = 4980;
	while (ng - ok > 1) {
		ll mid = (ok + ng) / 2;
		
		ll val = mid*mid*mid*mid*mid + A * mid - B * C;
		if (val <= 0) ok = mid;
		else ng = mid;
	}
	
	cout << ok / 1000 << '.' << ok % 1000 << '\n';
}