#include <bits/stdc++.h>

#define nl '\n'
#define ll long long int

using namespace std;

//* Use this for USACO Problems
void setIO(string s)
{
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}

double n;
bool test(double k)
{
    return k * k + sqrt(k) >= n;
}

int main()
{
    // setIO("circlecross");
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    // cin >> t;

    while (t--)
    {
        cin >> n;
        double l, r, m;
        l = 0;
        r = 1e10;
        for (int i = 0; i < 100; ++i)
        {
            m = (l + r) / 2;
            if (test(m))
            {
                r = m;
            }
            else
            {
                l = m;
            }
        }
        cout << setprecision(20) << l << nl;
    }
}