TP02E03

import java.util.Scanner;
import java.util.Stack;

public class PuntoTres {

    Scanner scanner = new Scanner(System.in);
    public static void main(String[] args) {
        PuntoTres myApp = new PuntoTres();

        myApp.run();

    }

    Stack<Long> divisorsOfN(Long n)
    {
        Stack<Long> ret = new Stack<Long>();
        for(long i = 1; i*i <= n; i++)
        {
            if(n%i == 0)
            {
                ret.push(i);
                if(n/i != i) ret.push(n/i);
            }
        }
        return ret;
    }

    long forceReadLong()
    {
        long n = 0;
        while(true)
        {
            try
            {
                System.out.println("Introduzca el valor de N:");
                n = Long.parseLong(scanner.next());
                return n;
            }
            catch(Exception ex)
            {
                System.out.println("Se introdujo un número inválido, reintente.");
            }
        }
    }

    boolean checkPerfectNumber(Long n, Stack<Long> divisors)
    {
        Long sumOfDivs = 0*1L;
        while(!divisors.isEmpty()) sumOfDivs+=divisors.pop();
        return sumOfDivs-n == n;
    }

    void run()
    {
        Long n = forceReadLong();
        Stack<Long> divisors = divisorsOfN(n);
        System.out.println(checkPerfectNumber(n, divisors) ? "Es número perfecto." : "No es número perfecto.");
    }

}