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: Wrong Answer)

using System;
using System.Text.RegularExpressions;
class Program
{
	static void Main(string[] args)
	{
		string[] kazu = Console.ReadLine().Split(' ');
      	int n = int.Parse(kazu[0]);
		int k = int.Parse(kazu[1]);
		string s = Console.ReadLine();
      
      	char c1 = s[k-1];
      	string s1 = c1.ToString();
      	string upper = s1.ToLower();
      	var re = new Regex(s1);
      	string s2 = re.Replace(s, upper, 1);
		//出力
		Console.WriteLine(s2);
	}
}