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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

var sc = bufio.NewReaderSize(os.Stdin, 1024*1024*1)

func main() {
	list := getStdinIntArr()
	N := list[0]
	K := list[1]
	S := getStdin()

	rtn := ""
	for i := 0; i < N; i++ {
		if i != K-1 {
			rtn += S[i : i+1]
		} else {
			switch {
			case S[i] == 'A':
				rtn += "a"
			case S[i] == 'B':
				rtn += "b"
			case S[i] == 'C':
				rtn += "c"
			case S[i] == 'a':
				rtn += "A"
			case S[i] == 'b':
				rtn += "B"
			case S[i] == 'c':
				rtn += "C"
			}
		}
	}

	fmt.Printf("%s\n", rtn)
}

func getStdin() string {
	return readLine()
}
func getStdinInt() int {
	str := getStdin()
	rtn, _ := strconv.Atoi(str)
	return rtn
}
func getStdinIntArr() []int {
	str := getStdin()
	list := strings.Split(str, " ")
	rtn := make([]int, len(list))
	for idx, val := range list {
		rtn[idx], _ = strconv.Atoi(val)
	}
	return rtn
}

func getStdinIntArr64() []int64 {
	str := getStdin()
	list := strings.Split(str, " ")
	rtn := make([]int64, len(list))
	for idx, val := range list {
		rtn[idx], _ = strconv.ParseInt(val, 10, 64)
	}
	return rtn
}

func readLine() string {
	buf := make([]byte, 0, 1024*1024*10)
	for {
		l, p, e := sc.ReadLine()
		if e != nil {
			panic(e)
		}
		buf = append(buf, l...)
		if !p {
			break
		}
	}
	return string(buf)
}