1. 
/*
 * ACM Contest training
 * Problem: 11466 - Largest Prime Divisor
 * Link: http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&category=26&problem=2461&mosmsg=Submission+received+with+ID+8383065
 *
 * @author Christoph Goettschkes
 * @version 1.0, 11/08/2010
 *
 * Method : Sieve of Eratosthenes
 * Status : Accepted
 * Runtime: 1.388
 */

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

class Main
{
	static List<Integer> primes = new LinkedList<Integer>();

	public static void main(String[] args) throws IOException
	{
		// max input has not more than 14 digits. Math.sqrt(10**14-1) = 9999999.9...
		sieve(9999999);

		BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

		long cur = Long.parseLong(reader.readLine());

		while (cur != 0) {
			if (cur == 1 || cur == -1)
				System.out.println(-1);
			else
				System.out.println(factor(Math.abs(cur)));
			cur = Long.parseLong(reader.readLine());
		}
	}

	public static long factor(long n)
	{
		Set<Long> set = new HashSet<Long>();

		for(int p : primes) {
			while (n % p == 0) {
				set.add((long)p);
				n /= p;
			}
			if (p > n)
				break;
		}

		if (n > 1)
			set.add(n);

		return set.size() == 1 ? -1 : Collections.max(set);
	}

	public static void sieve(int upperBound) {
		long last = 0;

		long upperBoundSquareRoot = (int) Math.sqrt(upperBound);
		BitSet isComposite = new BitSet(upperBound);

		for (long m = 2; m <= upperBoundSquareRoot; m++) {
			if (!isComposite.get((int)m)) {
				primes.add((int)m);
				last = m;
				for (long k = m * m; k <= upperBound; k += m) {
					isComposite.set((int)k, true);
				}
			}
		}

		if (upperBoundSquareRoot == last)
			upperBoundSquareRoot++;

		for (int m = (int)upperBoundSquareRoot; m <= upperBound; m++) {
			if (!isComposite.get(m)) {
				primes.add(m);
			}
		}
	}
}