import java.util.*;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int k = sc.nextInt();
    String str = sc.next();
    char[] c = new char[n];

    for (int i = 0 ; i < n ; i++ ) {
      c[i] = str.charAt(i);
    }

    if (c[k-1] == 'A') {
      c[k-1] = 'a';
    }

    if (c[k-1] == 'B') {
      c[k-1] = 'b';
    }

    if (c[k-1] == 'C') {
      c[k-1] = 'c';
    }

    for (int i = 0 ; i < n ; i++ ) {
      System.out.print(c[i]);
    }
  }
}

/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