import java.io.*;

class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		BufferedReader r = new BufferedReader (new InputStreamReader (System.in));
		String s1 = r.readLine();
		int index = Integer.valueOf(s1.split(" ")[1]) - 1;
		char[] s2 = r.readLine().toCharArray();
		char c = s2[index];
		s2[index] = Character.isUpperCase(c) ? Character.toLowerCase(c) : Character.toUpperCase(c);
		System.out.println(new String(s2));
	}
}
/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