#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int main() {
int a[105], n;
char s[105];
scanf("%s", s);
for(int i=0, j=0; i<strlen(s); i+=2, j++) a[j]=s[i]-48, n=j;
n++;
sort(a, a+n);
for(int i=0; i<n-1; i++) printf("%d+", a[i]);
printf("%d", a[n-1]);
return 0;
}
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