/*
* @Author Silviase(@silviasetitech)
* For ProCon
*/

import java.util.*;
import java.lang.*;
import java.math.*;

public class Main{    
    static int n;
    static int[] x = new int[n];
    static int[] y = new int[n];
    static int[] z = new int[n];
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        int k = sc.nextInt();
        int n = sc.nextInt();

        String s = sc.next();
        for (int i = 0; i < s.length(); i++) {
            if (i == n-1) {
                String a = s.substring(n-1, n);
                a = a.toLowerCase();
                System.out.print(a);
            }else{
                System.out.print(s.charAt(i));
            }
        }
        System.out.println("");

        sc.close();
    }

}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz