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.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace ConsoleApp1
{
    using static Util;

    internal class Program
    {

        static void Main(string[] args)
        {
            var k = ReadIntArray()[1];
            var s = Console.ReadLine();
            var res = string.Join("", s.Select((x, idx) => idx == k + 1 ? x.ToString().ToLower() : x.ToString()).ToArray());
            Console.WriteLine($"{res}");
#if DEBUG
            Console.Read();
#endif
        }
    }

    public static class Util
    {
        public static long[] ReadLongArray() => Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
        public static int[] ReadIntArray() => Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
        public static long ReadLong() => long.Parse(Console.ReadLine());
        public static long ReadInt() => int.Parse(Console.ReadLine());
    }
}