import java.util.Scanner;
class Main {
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        int n=in.nextInt();
        char ar[]= new char[n];
        int k=in.nextInt();
        ar=in.next().toCharArray();
        char ch=Character.toLowerCase(ar[k-1]);
        ar[k-1]=ch;
        for(char x:ar)
        {
            System.out.print(x);
        }    
    }
}

/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