#nullable enable

#region
var (_input, _iter) = (Array.Empty<string>(), 0);
T I<T>() where T : IParsable<T>
{
    while (_iter >= _input.Length) (_input, _iter) = (Console.ReadLine()!.Split(' '), 0);
    return T.Parse(_input[_iter++], null);
}
#endregion

Int128 k1 = 1000;
var k4 = k1 * k1 * k1 * k1;
var k5 = k4 * k1;

var c = I<Int128>();
c *= k5;
Int128 pass = 0;
Int128 fail = 10000000;
while (fail - pass > 1)
{
    var x = (fail + pass) >> 1;
    var y = x * x * x * x * x + x * k4;
    if (y <= c) pass = x;
    else fail = x;
}
var ans = (decimal)pass / 1000;
Console.WriteLine(ans.ToString("F3"));