#include <iostream>
#include <sstream>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <numeric>
#include <vector>
#include <string>
#include <set>
#include <map>

using namespace std;
#define ll long long
void sherry()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
bool comp(pair<int, int> a, pair<int, int> b)
{
    return a.second < b.second;
}
int main()
{
    sherry();
    string s;
    map<char, int> m;
    cin >> s;
    for (ll i = 0; i < s.size(); i++)
    {
        m[s[i]]++;
    }
    for (ll i = 0; i < s.size(); i++)
    {
        if (m[s[i]] % 2 == 1)
        {
            cout << s[i];
            m[s[i]] = 0;
        }
    }
}