#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <iterator>
using namespace std;
int main(){
    int n,t,b;

    string s;
    cin >> n;
    getline(cin, s);
    while(n--){
        getline(cin, s);
        t = s.length();
        int k=97;

        for(int i=0;i<t;i++){
            if(s[i] >='A' && s[i] <='Z')
                s[i] = s[i] + 32;
        }

        vector< pair<char,int> > v(26);

        for( vector< pair<char,int> >::iterator it1 = v.begin(); it1 != v.end(); it1++ ){
            it1->first = k++;
            it1->second = 0;
        }

        for(int it = 0; it < s.size(); it++){
            if(s[it] >='a' && s[it]<='z'){
                for(vector< pair<char,int> >::iterator it1 = v.begin(); it1 != v.end(); it1++){
                    if(it1->first == s[it])
                        it1->second++;
                }
            }
        }

        b = v.begin()->second;
        for(vector< pair<char,int> >::iterator it1 = v.begin(); it1 != v.end(); it1++){
            if(it1->second > b){
                b = it1->second;
            }
        }

        vector<char> p;
        for(vector< pair<char,int> >::iterator it1 = v.begin(); it1 != v.end(); it1++){
            if(it1->second == b)
                p.push_back(it1->first);
        }
        sort(p.begin(), p.end());
        for(int i=0;i<p.size();i++)
            cout << p.at(i);
        cout << endl;

    }
return 0;
}