Problem:
Score : 700 points

Problem Statement

Given is a sequence of N digits a_1a_2\ldots a_N, where each element is 1, 2, or 3.
Let x_{i,j} defined as follows:

x_{1,j} := a_j \quad (1 \leq j \leq N)

x_{i,j} := | x_{i-1,j} - x_{i-1,j+1} | \quad (2 \leq i \leq N and 1 \leq j \leq N+1-i)

Find x_{N,1}.

Constraints

2 \leq N \leq 10^6

a_i = 1,2,3 (1 \leq i \leq N)

Input

Input is given from Standard Input in the following format:

N
a_1a_2\ldotsa_N

Output

Print x_{N,1}.

Sample Input 1

4
1231

Sample Output 1

1

x_{1,1},x_{1,2},x_{1,3},x_{1,4} are respectively 1,2,3,1.

x_{2,1},x_{2,2},x_{2,3} are respectively |1-2| = 1,|2-3| = 1,|3-1| = 2.

x_{3,1},x_{3,2} are respectively |1-1| = 0,|1-2| = 1.

Finally, x_{4,1} = |0-1| = 1, so the answer is 1.

Sample Input 2

10
2311312312

Sample Output 2

0

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;

namespace G043
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());
            var nums = new int[N];

            var input = Console.ReadLine();
            for (int i = 0; i < N; i++)
            {
                nums[i] = int.Parse(input[i].ToString());
            }

            Console.WriteLine(Calc(nums));
        }

        private static int Calc(int[] arr)
        {
            var result = new int[arr.Length - 1];
            for (int i = 0; i < result.Length; i++)
            {
                result[i] = Math.Abs(arr[i] - arr[i+1]);
            }

            if (result.Length > 1)
            {
                if (result[result.Length - 1] == 0 && result[result.Length - 2] == 0 
                    && result[result.Length - 3] == 0)
                {
                    return 0;
                }
                return Calc(result);
            }
            else
            {
                return result[0];
            }
        }
    }
}