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

public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.print("Enter IPv6 address: ");
        String ip = sc.nextLine();
        
        if (isValidIPv6(ip)) {
            System.out.println("Valid IPv6 address");
        } else {
            System.out.println("Invalid IPv6 address");
        }
    }
    
    public static boolean isValidIPv6(String ip) {
        String[] parts = ip.split(":");
        
        if (parts.length != 8) {
            return false;
        }
        
        for (int i = 0; i < parts.length; i++) {
            String part = parts[i];
            
            if (part.length() == 0 || part.length() > 4) {
                return false;
            }
            
            for (int j = 0; j < part.length(); j++) {
                char c = part.charAt(j);
                
                if (!(c >= '0' && c <= '9' || 
                      c >= 'a' && c <= 'f' || 
                      c >= 'A' && c <= 'F')) {
                    return false;
                }
            }
        }
        
        return true;
    }
}