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;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using static System.Math;

namespace AtCorder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var l = Console.ReadLine()
               .Split(' ')
               .Select(int.Parse)
               .ToArray();
            var n = l[0];
            var k = l[1];
            var s = Console.ReadLine();
            var s2 = new string(s
                .Select((c, i) => (i + 1 == k) ? (char)(c - 'A' + 'a') : c)
                .ToArray());
            Console.WriteLine(s2);
        }
    }
}