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: Runtime Error)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace Contest
{
    struct Edge
    {
        public int U, V;
        public int Dist;

        public Edge(int u, int v, int w)
        {
            U = u;
            V = v;
            Dist = w;
        }
    }
    class Program
    {
        private int N;
        private List<Edge>[] Edges;
        private long[] Dist;
        public void Solve()
        {
            var sc = new Scanner();
            N = sc.NextInt();
            Edges = new List<Edge>[N];
            for (int i = 0; i < N; i++)
            {
                Edges[i] = new List<Edge>();
            }
            for (int i = 0; i < N - 1; i++)
            {
                int u = sc.NextInt() - 1;
                int v = sc.NextInt() - 1;
                int w = sc.NextInt();
                Edges[u].Add(new Edge(u, v, w));
                Edges[v].Add(new Edge(v, u, w));
            }
            Dist = new long[N];
            for (int i = 0; i < N; i++)
            {
                Dist[i] = -1;
            }
            var q = new Queue<int>();
            Dist[0] = 0;
            q.Enqueue(0);
            while (q.Count > 0)
            {
                int n = q.Dequeue();
                foreach (Edge edge in Edges[n])
                {
                    if (Dist[edge.V] == -1)
                    {
                        Dist[edge.V] = Dist[n] + edge.Dist;
                        q.Enqueue(edge.V);
                    }
                }
            }

            Console.WriteLine(string.Join("\n", Dist.Select(i => i % 2)));
        }

        static void Main() => new Program().Solve();
    }
}

class Scanner
{
    public Scanner()
    {
        _stream = new StreamReader(Console.OpenStandardInput());
        _pos = 0;
        _line = new string[0];
        _separator = ' ';
    }
    private char _separator;
    private StreamReader _stream;
    private int _pos;
    private string[] _line;
    #region get a element
    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = _stream.ReadLine().Split(_separator);
            _pos = 0;
        }
        return _line[_pos++];
    }
    public int NextInt()
    {
        return int.Parse(Next());
    }
    public long NextLong()
    {
        return long.Parse(Next());
    }
    public double NextDouble()
    {
        return double.Parse(Next());
    }
    #endregion
    #region convert array
    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }
    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }
    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }
    #endregion
    #region get array
    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = _stream.ReadLine().Split(_separator);
        _pos = _line.Length;
        return _line;
    }
    public int[] IntArray()
    {
        return ToIntArray(Array());
    }
    public long[] LongArray()
    {
        return ToLongArray(Array());
    }
    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }
    #endregion
}