import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        
        int N = scanner.nextInt();
        int K = scanner.nextInt();
        
        String S = null;
        
        S = scanner.next();
        
        int count;
        String small = "";
        
        for(count=0 ; count < S.length() ; count++){
            if(count == K - 1){
                small += String.valueOf(S.charAt(count)).toLowerCase();
            }else{
                small += String.valueOf(S.charAt(count));
            }
        }
        
        System.out.println(small);
        
    }
}
/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