#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
 
const int MOD=1e9+7;
const int INF=LLONG_MAX/2;
 
signed main() {
   ios::sync_with_stdio(false);cin.tie(NULL);
   string s;
   cin>>s;
   vector<char>arr;
   for(int i=0;s[i]!='\0';i++){
   	if(s[i] != '+')arr.push_back(s[i]);
   }
   sort(arr.begin(),arr.end());
   for(int i=0;i<arr.size();i++){
   	if(i==0)cout<<arr[i];
   	else cout<<'+'<<arr[i];
   }
 
 
}

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Mgo=

2