using System;

public class Program

{

    public static void Main()

    {

        int n = 16;

        int k = 1;

        double sum = 0;

        double res;

        for(; k < n; k++){

            res = Eq(n, k);

            //Console.WriteLine(res);

            sum += res;

        }

        Console.WriteLine(sum);

    }

    public static double Eq(int n, int k){

        double res = Fac(n) / (Fac(k) * Fac(n-k));

        return res;

    }

    public static double Fac(int i){

        double sum = i;

        for(int j = i - 1; j > 1; j--){

            sum *= j;

        }

        return sum;

    }

}