#include<bits/stdc++.h>
using namespace std;
#define fastio ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
vector<long long>prime;
bool x[10000007];
void seieve()
{
    x[0]=1;
    x[1]=1;
    prime.push_back(2);
    for(int i=3; i*i<=10000005; i+=2)
    {
        if(!x[i])
        {
            for(int j=i*i; j<=10000005; j+=2*i)
            {
                x[j]=1;
            }
        }
    }
    for(int i=3; i<=10000005; i+=2)
        if(!x[i])
            prime.push_back(i);
}
int main()
{
    //fastio;
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    seieve();
    long long a,b,c,d,i,j,n,m;
    cin>>n;
    while(n)
    {
        n=abs(n);
        a=0;
        b=-1;
        m=n;
        c=0;
        while(a<prime.size()&&n>1&&prime[a]*prime[a]<=n)
        {
            if(n%prime[a]==0)
                c++;
            while(n%prime[a]==0)
            {
                b=max(b,prime[a]);
                n/=prime[a];
            }
            a++;
        }
        if(n>1&&m!=n)
        {
            c++;
            b=max(b,n);
        }
        if(c<=1)
            b=-1;
        cout<<b<<'\n';
        cin>>n;
    }
    return 0;
}