t1

#include <iostream>
#include <map>
using namespace std;
int main() {
    map<char, int> word;
    char letter;
    while(cin >> letter)
        ++word[letter];
    for (auto it = word.begin(); it != word.end(); ++it) {
        if (it->second > 1)
            cout << it->first;
    }
    return 0;
}