#include <bits/stdc++.h>
using namespace std;

using  ll =          long long int;
using ull = unsigned long long int;
const char en ='\n';
const int  mod=1000000007;

int main(){
	cin.tie();
	ios::sync_with_stdio(false);

	string s;cin>>s;
	priority_queue<char> q;

	//s="114514";

	for(ull i=0;i<s.size();i++){
		q.push(s[i]);
	}
	while(!q.empty()){
		cout<<q.top();
		q.pop();
	}
	cout<<en;
	return 0;
}