#include<bits/stdc++.h>
#include<iostream>
#include<cstring>
using namespace std;
int main()
{
string s;
string a="";
int b,temp,i,j;
cin>>s;
j=0;
if(s.size()==1)
{
cout<<s;
return 0;
}
for(i=0;i<s.size();i=i+2)
{
//cout<<"i= "<<i<<endl;
a+=s[i];
j++;
}
//cout<<"A array: "<<a<<endl;
b=a.size();
for(j=0;j<b;j++)
{
for(i=j+1;i<b;i++)
{
if(a[j]>a[i])
{
temp=a[j];
a[j]=a[i];
a[i]=temp;
}
}
}
j=0;
for(i=0;i<s.size();i=i+2)
{
s[i]=a[j];
j++;
}
//cout<<"A array: "<<a<<endl;
cout<<s;
return 0;
}
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