import java.util.*;

public class Main {
    
    public static void main(String[] args) throws Exception {
        
        Scanner sc = new Scanner(System.in);
        
        sc.nextInt();
        int n = sc.nextInt() -1;
        String target = sc.next();
        
        char c = (char)((int)target.charAt(n) - (int)('A'-'a'));
        char[] targetChars = target.toCharArray();
        targetChars[n] = c;
        
        System.out.println(String.valueOf(targetChars));
        
    }
}

/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