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

class yuki319
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(int n) => Enumerable.Repeat(0, n).Select(_ => NList).ToArray();
    static void Main()
    {
        var n = NN;
        var a = NList;
        var list = LCT(a);
        if (Check(list))
        {
            WriteLine(list.Last());
        }
        else
        {
            WriteLine(0);
        }
    }
    static bool Check(List<int> list)
    {
        if (list.Count == 1) return true;
        for (var i = 1; i < list.Count; i += 2) if (list[i] != 0) return false;
        if (list[0] == 0 || list[2] == 0 || list[0] == list[2]) return false;
        for (var i = 4; i < list.Count; i += 4) if (list[0] != list[i]) return false;
        for (var i = 6; i < list.Count; i += 4) if (list[2] != list[i]) return false;
        return true;
    }
    static List<int> LCT(int[] list)
    {
        var nl = new List<int>(list.Length - 2);
        for (var i = 0; i < list.Length - 2; ++i)
        {
            if (list[i] == (list[i + 1] + 1) % 3 && list[i] == (list[i + 2] + 2) % 3) nl.Add(2);
            else if (list[i + 1] == (list[i] + 1) % 3 && list[i + 2] == (list[i] + 2) % 3) nl.Add(1);
            else nl.Add(0);
        }
        return nl;
    }
}