import java.util.*;
import java.lang.*;
import java.io.*;

// The main method must be in a class named "Main".
class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
        
        int i = 4;
        int j = 5;
        int swap;
        swap = i;
        i = j;
        j = swap;
        System.out.print(i);
        System.out.print(j);
    }
}