using System;

public class Hello
{
    static void Main()
    {
        var p = double.Parse(Console.ReadLine().Trim());
        if (p == 0) { Console.WriteLine(0); goto exit; }
        var r = 1d;
        var res = 0d;
        while (r > 0.00001)
        {
            r *= p;
            res += r;
        }
        Console.WriteLine(res);
    exit:;
    }
}