#include<iostream>
#include<stdio.h>
#include<algorithm>

using namespace std;

int main(){

    string str;
    cin>> str;

    sort(str.begin(), str.end());

    auto itr = str.end()-1;
    for(; itr!=str.begin()-1; itr--){
        cout<< *itr;
    }
    cout<< endl;


    return 0;
}