Problem:
Score : 100 points

Problem Statement

We have a 3×3 square grid, where each square contains a lowercase English letters.
The letter in the square at the i-th row from the top and j-th column from the left is c_{ij}.

Print the string of length 3 that can be obtained by concatenating the letters in the squares on the diagonal connecting the top-left and bottom-right corner of the grid, from the top-left to bottom-right.

Constraints

Input consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

c_{11}c_{12}c_{13}
c_{21}c_{22}c_{23}
c_{31}c_{32}c_{33}

Output

Print the string of length 3 that can be obtained by concatenating the letters on the diagonal connecting the top-left and bottom-right corner of the grid, from the top-left to bottom-right.

Sample Input 1

ant
obe
rec

Sample Output 1

abc

The letters in the squares on the diagonal connecting the top-left and bottom-right corner of the grid are a, b and c from top-right to bottom-left. Concatenate these letters and print abc.

Sample Input 2

edu
cat
ion

Sample Output 2

ean

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Numerics;

namespace Atcoder {
    class Program {
        static void Main(string[] args) {
            //var N = int.Parse(Console.ReadLine());
            //var inputList = new List<int>();
            //foreach (var i in Enumerable.Range(0, N))
            //    inputList.Add(int.Parse(Console.ReadLine()));


            var NM = Console.ReadLine().Split(' ');
            var N = int.Parse(NM.First());
            var M = int.Parse(NM.Last());

            var result = 0;
            if (N == 1 && M == 1)
                result = 1;
            if ((N == 1 && M > 1) || (N > 1 && M == 1))
                result = N * M - 2;
            else if (N >= 2 && M >= 2)
                result = (N - 2) * (M - 2);

            if (result < 0)
                result = 0;

            Console.WriteLine(result);

            //var NK = Console.ReadLine().Split(' ');
            //var N = int.Parse(NK.First());
            //var K = int.Parse(NK.Last());

            //long count = 0;
            ////count += (N - K - 1) * (N - K);
            //count += Factorial(N - K);
            //if (K == 0)
            //    count += N;
            //else
            //    for (int a = K; a < N; a++) {
            //        for (int b = K; b < a; b++) {
            //            if (a % b == 0) {
            //                // Console.WriteLine("{0} {1}", a, b);
            //                count++;
            //            }
            //        }
            //    }
            //Console.WriteLine(count);
            return;
        }

        //public static BigInteger Factorial(int n) {
        //    if ((n & 1) == 0) return Factorial(n / 2).Square() * Combination(n, n / 2);
        //    else return Factorial(n / 2).Square() * Combination(n, n / 2) * (n - n / 2);
        //}
    }
}