Big_Prime

// In the name of Allah.
// We're nothing and you're everything.
// Ya Ali!
/*
                  ,     \    /      ,
                 / \    )\__/(     / \
                /   \  (_\  /_)   /   \
           ____/_____\__\@  @/___/_____\____
          |             |\../|              |
          |              \VV/               |
          |        ------___-------         |
          |__________Chuta Dragon___________|
           |    /\ /      \\       \ /\    |
           |  /   V        ))       V   \  |
           |/     `       //        '     \|
           `              V                '
        */

#include<bits/stdc++.h>
using namespace std;
typedef  long long ll;
typedef pair<ll,ll>pll;
#define fastread() (ios_base:: sync_with_stdio(false),cin.tie(NULL))
#define fi first
#define se second
#define pb push_back
///-------------------------------------------------------------------------------------------------///
///                KARMA IS LIKE 69,,, YOU GET WHAT YOU GIVE                                        ///
///-------------------------------------------------------------------------------------------------///
void input(ll ara[],ll n)
{
    for(ll i=0; i<n; i++)
        cin>>ara[i];
}

void output(ll ara[],ll n)
{
    for(ll i=0; i<n; i++)
        cout<<ara[i]<<" ";
}

#define eb emplace_back

const int N=1e7;
ll k;
//bitset<N+10>ara;

ll ara[N+10];

vector<ll>v;

void sieve()
{
      ara[0]=1;
      ara[1]=1;

      v.pb(2);

      int i,j,sz=sqrt(N);

      for(i=2; i<=sz; i++)
      {
          if(ara[i]==0)
          {
              v.push_back(i);

              for(j=i*2; j<=N; j+=i)
              {
                  ara[j]=1;

              }
          }
      }


     for(ll i=sz+1; i<=N; i++)
    {
        if(ara[i]==0)
        {
            v.pb(i);
        }
    }

      k=v.size();

}
ll prime(ll t)
{
    if(t<=N)
    {
      if(ara[t]==0)return 1;//prime
      else return 0;// a[0]=1 mana not prime
    }
    else
    {
    ll m=sqrt(t);
    //condi:1(i<k) mana vcetor or full ar modda na takla prime must;
    //condi:1(v[i]<=m) mana vector ar any value jodi sqrt(t) ar boro hala prime  must (it is a prime low)
    for(ll i=0;i<k && v[i]<=m;i++)
    {
        if(t%v[i]==0)return 0;
    }
    return 1;

    }



}



int main()
{

   sieve();// suru ta e sieve must (void funtion must call)
ll n;

   while(cin>>n && n)
   {

        n=abs(n);


       ll mx=-1,cnt=0;
 ll len=sqrt(n);

       for(ll i=2;i<=len;i++)
       {
           if(n%i==0)
           {
               if(prime(i))
               {
                   cnt++;
                  mx=max(i,mx);
               }

               if(prime(n/i) && n/i!=i)//n/i!=9 must coz 9=3,3
               {
                   cnt++;
                   mx=max(n/i,mx);
               }
           }
       }

       if(cnt<2)cout<<-1<<endl;
       else cout<<mx<<endl;



   }






}