import java.util.*;
import java.io.*;

public class Main {
	private static void solve(){
	//Implement solution here.
		int n = ni();
		int k = ni();
		char[] ca = next().toCharArray();
		ca[k-1] = Character.toLowerCase(ca[k-1]);
		System.out.println(new String(ca));
	}

    //Switch input source (stdin/file)
	private static BufferedReader br  = new BufferedReader(new InputStreamReader(System.in));
	public static void main(String[] args){
        String debugDataPath = System.getenv("DD_PATH");        
        if(debugDataPath != null){
            try{
            	br = new BufferedReader(new InputStreamReader(new FileInputStream(new File(debugDataPath))));
            }catch(Exception e){
                throw new RuntimeException(e);
            }
        }
        solve();
	}

    //Input read utility
	private static StringTokenizer tokenizer = null;
	public static String next() {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(br.readLine());
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}
    //Get next single int
	private static int ni() {
		return Integer.parseInt(next());
	}
    //Get next single long
	private static long nl() {
		return Long.parseLong(next());
	}
    //Get next single double
	private static double nd() {
		return Double.parseDouble(next());
	}
    //Get next int array from one line
	private static int[] na(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = ni();
		return a;
	}
	//Get next char array from one line
	private static char[] ns() {
		return next().toCharArray();
	}
    //Get next long array from one line
	private static long[] nal(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nl();
		return a;
	}
}
/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