#include <cstring>
#include <algorithm>
#include <iostream>
#include <fstream>

using namespace std ;

char x[231];
int compare (const void * a, const void * b)
{
    return *(char*)a-*(char*)b;
}

void reverse(char word[])
{
    int len=strlen(word);
    for (int i=0;i<len/2;i++)
    {
        word[i]^=word[len-i-1];
        word[len-i-1]^=word[i];
        word[i]^=word[len-i-1];
    }
}

int main()
{
    char x2[231];
    char x3[231];
    scanf("%300s",x);

    if (strlen(x) % 2 == 0)
    {
        strncpy(x2,x,strlen(x)/2);
        qsort (x2,strlen(x2),1,compare);
        reverse(x2);

        strncpy(x3,x,strlen(x)/2);
        qsort (x3,strlen(x3),1,compare);

        cout << x2 << x3;
    }
    else if (strlen(x) % 2 != 0)
    {
    int lenght = strlen(x);
        int t1 = lenght/2;

        strncpy(x2,x,strlen(x)/2);
        qsort (x2,strlen(x2),1,compare);
        reverse(x2);

    strncpy(x3,x,strlen(x)/2);
        qsort (x3,strlen(x3),1,compare);

        cout << x2 << x[(strlen(x)/2)] << x3;
    }
}