What is the issue in the code
package com.codegym.task.task07.task0720;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
/*
Shuffled just in time
*/
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
//write your code here
int N = Integer.parseInt(reader.readLine());
int M = Integer.parseInt(reader.readLine());
ArrayList<String> sList = new ArrayList<String>();
for (int i=0; i<N; i++) {
sList.add(reader.readLine());
}
for (int i=0; i < M; i++) {
Collections.swap(sList,i, M+i);
}
for (String s: sList) {
System.out.println(s);
}
}
}