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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php
class MyTest {

    private function getInput() {
        while (!empty($input = fgets(STDIN))) {
            $ret[] = trim($input);    
        }
        return $ret;
    }

    private function main($input) {
        $line1 = explode(' ', $input[0]);
        $n = $line1[0];
        $k = $line1[1];
        $str = $input[1];
        $ret = '';
        for($i = 0; $i < $n;  $i++){
            if ($i == $k - 1) {
                $txt = strtolower($str[$i]);
            } else {
                $txt = $str[$i];
            }
            $ret .= $txt;
        }
        echo $ret;
    }

    public function run() {
        $input = self::getInput();
        self::main($input);
    }
    
}

MyTest::run();