static double Fact(int a)
        {
            double F = 1;
            for (int i = 1; i <= a; i++)
            {
                F *= i;
            }
            return F;
        }
        static void Main(string[] args)
        {
            int n = int.Parse(ReadLine());
            int k = int.Parse(ReadLine());
            double C = Fact(n) / (Fact(k) * Fact(n - k));
            WriteLine(C);
        }