Problem:
Score : 100 points

Problem Statement

Given is a lowercase English letter C that is not z. Print the letter that follows C in alphabetical order.

Constraints

C is a lowercase English letter that is not z.

Input

Input is given from Standard Input in the following format:

C

Output

Print the letter that follows C in alphabetical order.

Sample Input 1

a

Sample Output 1

b

a is followed by b.

Sample Input 2

y

Sample Output 2

z

y is followed by z.

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

using System;
using System.Linq;

public class AtCoder_151_E
{
    public static int[,] ncm;

    public static void Main()
    {
        //var exStdIn = new System.IO.StreamReader("input.txt");
        //System.Console.SetIn(exStdIn);

        long mod = 1000000007;

        int[] nums = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
        int n = nums[0];
        int k = nums[1];

        int[] c = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).OrderBy(i => i).ToArray();

        ncm = new int[n,n];
        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < n; j++)
            {
                ncm[i, j] = -1;
            }
        }

        long sum = 0;
        for (int i = 0; i < n - k + 1; i++)
        {
            for (int j = i + k - 1; j < n; j++)
            {
                long add = c[j] - c[i];
                if (j - i >= 2)
                {
                    add *= nCm(j - i - 1, k - 2);
                    add %= mod;
                }
                sum += add;
                sum %= mod;
            }
        }
        Console.WriteLine(sum);
    }

    public static int nCm(int n, int m)
    {
        if (ncm[n, m] != -1)
        {
            return ncm[n, m];
        }
        if (m == 0)
        {
            ncm[n, m] = 1;
            return 1;
        }

        if (n == 0)
        {
            ncm[n, m] = 0;
            return 0;
        }
        ncm[n, m] = n * nCm(n - 1, m - 1) / m;
        return ncm[n, m];
    }
}