#include <bits/stdc++.h>

using namespace std;

int main() {
    long double x0, xm, a, xn;
    //m = n + 1
    cin >> a;
    if (a <= 1) {
        if (2 * a <= 0.95)
            x0 = 2 * a;
        else
            x0 = 0.95;
    }
    else if (a > 1 && a <= 25) {
        x0 = a / 5;
    }
    else {
        x0 = a / 25;
    }
    xn = x0;
    xm = a * xn / 5 + 4 / (5 * pow(xn, 4));

    while (5 * a * abs(xm - xn) / 4 >= pow(10, -6)) {
        xn = xm;
        xm = a * xn / 5 + 4 / (5 * pow(xn, 4));
    }

    cout << a - pow(xn, 5);

    return 0;
}