#include <iostream>
#include <string>
#include <algorithm>
#include <map>
using namespace std;
int main() {
map<char, int> mapa;
string str;
cin >> str;
for (const auto& chr : str)
{
mapa[chr] += 1;
}
for (const auto& kv : mapa)
{
cout << kv.first;
}
return 0;
}
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