#include <iostream>
#include <algorithm>
#include <locale>

using namespace std;

int main() {
    string s, res = "";
    int* arr = new int[255];
    for (int i = 0; i < 255; i++)
        arr[i] = 0;
    cin >> s;
    for (int i = 0; i < s.size(); i++)
    {
        arr[s[i]]++;
        if (arr[s[i]] > 1)
            res += s[i];
    }
    cout << res;
    return 0;
}