#include <iostream>
#include <cstring>
using namespace std;
const int INF = 1007;
int main()
{
    char sequence[INF];
    int n = strlen(sequence);
    int x =0;

    for (int i = 0; i < n; i++)
    {
        cin >> sequence[i];
        if(i !=0 && i%2 == 0)
        {
            if(sequence[i] < sequence[i-2]&& i-2 >= 0)
            {
                swap(sequence[i],sequence[i-2]);
            }
        }
    }
    for (int i = 0; i < n; i++)
    {
        cout << sequence[i];
    }

}