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

void solve()
{
    vector<int> vc = {};
    vector<char> s;

    for (auto it : s)
    {
        cin >> it;

        if (it != '+')
        {
            vc.push_back(it);
        }
    }
    sort(vc.begin(), vc.end());
    for (auto it : vc)
    {
        cout << it << '+';
    }
}
int main()
{
    ll t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
}