Problem:
Score : 100 points

Problem Statement

You are given a string S of length N consisting of A, B and C, and an integer K which is between 1 and N (inclusive).
Print the string S after lowercasing the K-th character in it.

Constraints

1 ≤ N ≤ 50

1 ≤ K ≤ N

S is a string of length N consisting of A, B and C.

Input

Input is given from Standard Input in the following format:

N K
S

Output

Print the string S after lowercasing the K-th character in it.

Sample Input 1

3 1
ABC

Sample Output 1

aBC

Sample Input 2

4 3
CABA

Sample Output 2

CAbA

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.Text.RegularExpressions;
using System.Threading.Tasks;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
          	var input_B = Console.ReadLine()
                .ToCharArray().Select(i => int.Parse(i.ToString())).ToArray();
            var isMMYY_M0 = Regex.IsMatch(input_B[1].ToString(), @"[1-9]+$");
            var isMMYY_M1 = Regex.IsMatch(input_B[1].ToString(), @"[0-2]+$");
            var isYYMM_M0 = Regex.IsMatch(input_B[3].ToString(), @"[1-9]+$");
            var isYYMM_M1 = Regex.IsMatch(input_B[3].ToString(), @"[0-2]+$");

            var isMMYY = false;
            var isYYMM = false;
            if ((input_B[0] == 0 && isMMYY_M0) || (input_B[0] == 1 && isMMYY_M1))
                isMMYY = true;

            if ((input_B[2] == 0 && isYYMM_M0) || (input_B[2] == 1 && isYYMM_M1))
                isYYMM = true;

            if(isYYMM && isMMYY)
            {
                Console.WriteLine("AMBIGUOUS");
            }
            else if (isYYMM)
            {
                Console.WriteLine("YYMM");
            }
            else if (isMMYY)
            {
                Console.WriteLine("MMYY");
            }
            else
            {
                Console.WriteLine("NA");
            }
        }
    }
}