using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Text;
//using static CompLib.CompLib;
//using DataStructure;

namespace atcoder
{
    class Program
    {
        const int intMax = 1000000000;
        const long longMax = 2000000000000000000;
        static void Main(string[] args)
        {
           int N = int.Parse(Console.ReadLine());
            var A = Console.ReadLine().Split().Select(int.Parse).ToArray();
            long all = 0;
            for (int i = 1; i <= N; i++)
            {
                if (i == 1) all = i;
                else all *= i;
            }
            var list = new long[N + 1];
            for (int i = 0; i < N; i++)
            {
                list[A[i]]++;
            }
            long p = 1;
            for (int i = 0; i < N; i++)
            {
                if (list[i] > 0)
                {
                    for (long j = 1; j <= list[i]; j++)
                    {
                        p *= j;
                    }
                }
            }
            Console.WriteLine(all / p);
        }
    }
}