import java.io.*;
public class Main
{
    public static void main(String []args)throws IOException
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        String line = br.readLine();
        String []tokens = line.split(" ");
        int n = Integer.parseInt(tokens[0]);
        int K = Integer.parseInt(tokens[1]);
        String S=br.readLine();
        int p=S.charAt(K-1);
        char x=(char)(p+32);
System.out.print(S.substring(0,(K-1))+x+S.substring(K));
}
}

/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