#include <bits/stdc++.h>
#define MAXSIZE 10000001
#define ii long long int

using namespace std;

int prime_arraysize;
int status[MAXSIZE];
int prime[MAXSIZE]; // this will contain the primes

void seive() {

    /// status[i]==1 -> i is not prime
    /// status[i]==0 -> i is prime
    status[0]=1;
    status[1]=1;
    for(int i=4;i<=MAXSIZE;i+=2)
    {
        status[i]=1;
    }
    for (int p=3; p*p<=MAXSIZE; p+=2)
    {

        if (!status[p])
        {

            for (int i=p*p; i<=MAXSIZE; i += 2*p)
                status[i] = 1;
        }
    }

    prime_arraysize=0;
    for(int i = 2; i <= MAXSIZE; i++ ) {
        if( status[i] == 0 ) {
            // so, i is prime
            prime[prime_arraysize++]=i;
        }
    }
}

ii max(ii a,ii b)
{
    if(a>b)
        return a;
    else
        return b;
}

ii primeFactorize( ii n ) {
    ii sqrtN = (ii)( sqrt(n) );
    ii mm=0;
    int ff=0;
    for( int i = 0;i<prime_arraysize && prime[i] <= sqrtN; i++ ) {
        if( n % prime[i] == 0 ) {
            ff++;
            while( n % prime[i] == 0 ) {
                n /= prime[i];
                mm=max(mm,prime[i]);
            }
            sqrtN=(ii)(sqrt(n));
        }
    }
    if( n > 1 ) {
        ff++;
        mm=max(mm,n);
    }
    if(ff==1)
        return -1;
    return mm;
}

int main() {
//    freopen("in.txt","r",stdin);
//    freopen("out.txt","w",stdout);
    seive();
    ii N;
    while(scanf("%lld",&N)==1)
    {
        if(N==0)
            break;
        if(N==1)
        {
            printf("-1\n");
            continue;
        }
        ii ans=primeFactorize(N);
        if(ans!=N)
            printf("%lld\n",ans);
        else
            printf("-1\n");
    }
    return 0;
}