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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;

namespace AtCoder.Question
{
    public class QuestionA
    {
        public static void Main(string[] args)
        {
            var (n, k) = ReadHelper.ReadValue<int, int>();
            var s = ReadHelper.ReadValue<string>();
            Console.WriteLine(new string(s.Select((c, i) => (char)(i == k - 1 ? c + 32 : c)).ToArray()));
        }

        static class ReadHelper
        {
            internal static T ReadValue<T>()
            {
                return (T)Convert.ChangeType(Console.ReadLine(), typeof(T));
            }
            internal static (T1, T2) ReadValue<T1, T2>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)));
            }
            internal static (T1, T2, T3) ReadValue<T1, T2, T3>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)), (T3)Convert.ChangeType(input[2], typeof(T3)));
            }
            internal static (T1, T2, T3, T4) ReadValue<T1, T2, T3, T4>()
            {
                var input = Console.ReadLine().Split(' ');
                return ((T1)Convert.ChangeType(input[0], typeof(T1)), (T2)Convert.ChangeType(input[1], typeof(T2)), (T3)Convert.ChangeType(input[2], typeof(T3)), (T4)Convert.ChangeType(input[3], typeof(T4)));
            }
            internal static T[] ReadValues<T>()
            {
                var input = Console.ReadLine().Split(' ');
                return input.Select(x => (T)Convert.ChangeType(x, typeof(T))).ToArray();
            }
        }

        static class MathAlgorithm
        {
            internal static bool IsPrime(long n)
            {
                if (n == 2) return true;
                if (n < 2 || n % 2 == 0) return false;
                var sqrt = Math.Sqrt(n);
                for (int i = 3; i <= sqrt; i += 2) if (n % i == 0) return false;
                return true;
            }
            internal static IEnumerable<long> EnumeratePrimes(long n)
            {
                var i = 2L;
                while (i * i <= n)
                {
                    if (n % i == 0)
                    {
                        n /= i;
                        yield return i;
                    }
                    else
                    {
                        i += i == 2 ? 1 : 2;
                    }
                }
                if (n != 1) yield return n;
            }
        }
    }
}