#include <bits/stdc++.h>

#define ms(a,b)         memset(a,b,sizeof(a))
#define pb(a)           push_back(a)
#define db              double
#define ft              float
#define ll              long long
#define ull             unsigned long long
#define ff              first
#define ss              second
#define sz(x)           x.size()
#define qu              queue
#define pqu             priority_queue
#define vc              vector
#define vi              vector<int>
#define vll             vector<long long>
#define vs              vector<string>
#define pii             pair<int,int>
#define pis             pair<int,string>
#define psi             pair<string,int>
#define all(x)          x.begin(),x.end()
#define CIN             ios_base::sync_with_stdio(0); cin.tie(0)
#define loop0(i,n)      for(int i=0;i<n;i++)
#define loop1(i,n)      for(int i=1;i<=n;i++)
#define stlloop(x)     for(__typeof(x.begin()) it=x.begin();it!=x.end();it++)
#define gcd(a, b)       __gcd(a, b)
#define lcm(a, b)       ((a)*((b)/gcd(a,b)))
#define case(z,x)       cout<<"Case "<<i<<": "<<x<<endl
#define case(z)         cout<<"Case "<<z<<": "
#define PI              3.14159265358979323846264338328
#define valid(tx,ty)    tx>=0 && tx<r && ty>=0 && ty<c
#define MAX             2000

/*----------------------Graph Moves----------------*/
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*------------------------------------------------*/

using namespace std;

map<char,int> mp;
vector<char> v;

int main()
{
    CIN;
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);

    int t;
    cin>>t;
    loop1(z,t)
    {
        string s;
        cin>>s;
        loop0(i,sz(s))
        {
            mp[s[i]]++;
        }
        stlloop(mp)
        {
            int a=it->second;
            int b=0;
            if(a>1)
            {
                for(int j=2; j*j<=a; j++)
                {
                    if(a%j==0)
                    {
                        b=1;
                        break;
                    }
                }
                if(a==2 || b==0)
                    v.pb(it->first);
            }
        }
        cout<<"Case "<<z<<": ";
        if(sz(v)==0)
        {
            cout<<"empty"<<endl;
        }
        else
        {
            loop0(i,sz(v))
            {
                cout<<v[i];
            }
            cout<<endl;
        }
        v.clear();
        mp.clear();
    }
    return 0;
}