using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var m = NN;
        if (n == 0)
        {
            WriteLine("NaN");
            return;
        }
        if (m == 0 || n < m)
        {
            WriteLine(0);
            return;
        }
        var dp = new long[m + 1];
        for (var i = 1; i < dp.Length; ++i)
        {
            var sum = (long)Math.Pow(i, n);
            for (var j = 1; j <= i; ++j) sum -= dp[j] * NCR(i, j);
            dp[i] = sum;
        }
        WriteLine(dp[m]);
    }
    static long NCR(int n, int r)
    {
        var ans = 1L;
        for (var i = n - r; i < n; ++i) ans *= i + 1;
        for (var i = 0; i < r; ++i) ans /= i + 1;
        return ans;
    }
}