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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import java.io.*;
import java.text.*;
import java.math.*;
import static java.lang.Integer.*;
import static java.lang.Double.*;
import java.lang.Math.*;

public class Main {

	public static void main(String[] args) throws Exception {
		new Main().run();
	}

	public void run() throws Exception {
		FastIO file = new FastIO();
		int n = file.nextInt();
		int k = file.nextInt() - 1;
		String s = file.next();
		System.out.println(s.substring(0, k) + s.substring(k, k + 1).toLowerCase() + s.substring(k + 1));
	}

	public static class FastIO {
		BufferedReader br;
		StringTokenizer st;

		public FastIO() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
	}

	public static long pow(long n, long p, long mod) {
		if (p == 0)
			return 1;
		if (p == 1)
			return n % mod;
		if (p % 2 == 0) {
			long temp = pow(n, p / 2, mod);
			return (temp * temp) % mod;
		} else {
			long temp = pow(n, (p - 1) / 2, mod);
			temp = (temp * temp) % mod;
			return (temp * n) % mod;

		}
	}

	public static long pow(long n, long p) {
		if (p == 0)
			return 1;
		if (p == 1)
			return n;
		if (p % 2 == 0) {
			long temp = pow(n, p / 2);
			return (temp * temp);
		} else {
			long temp = pow(n, (p - 1) / 2);
			temp = (temp * temp);
			return (temp * n);

		}
	}

	public static long gcd(long x, long y) {
		if (x == 0)
			return y;
		else
			return gcd(y % x, x);
	}

	public static boolean isPrime(int n) {
		if (n <= 1)
			return false;
		if (n <= 3)
			return true;

		if (n % 2 == 0 || n % 3 == 0)
			return false;

		for (int i = 5; i * i <= n; i = i + 6)
			if (n % i == 0 || n % (i + 2) == 0)
				return false;

		return true;
	}
}