using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        double x = double.Parse(Console.ReadLine());
        double a1 = x * x * x * x / 2 / 3 / 4;
        double s0 = double.MinValue;
        double s1 = a1;
        for (int i = 1; Math.Abs(s1 - s0) > double.Epsilon; i++) {
            s0 = s1;
            a1 = a1 * -(x * x * x) / (3 * (i - 1) + 5) / (3 * (i - 1) + 6) / (3 * (i - 1) + 7);
            s1 = s0 + a1;
        }
        Console.WriteLine(s1);
    }
}