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: Accepted)

using System;

public class AtCoderA
{
    static void Main()
    {
        int n;
        int k;
        {
            var line = Console.ReadLine();
            var words = line.Split(' ');
            n = int.Parse(words[0]);
            k = int.Parse(words[1]);
        }

        string s = Console.ReadLine();

        string answer = "";
        for (int i = 0; i < n; i++)
        {
            string str = s.Substring(i, 1);
            if (i + 1 == k)
            {
                if ("A".Equals(str))
                {
                    answer += "a";
                }
                else if ("B".Equals(str))
                {
                    answer += "b";
                }
                else if ("C".Equals(str))
                {
                    answer += "c";
                }
            }
            else
            {
                answer += str;
            }
        }

        Console.WriteLine(answer);
    }
}