#include <cstdio>
using namespace std;

const int MAXSIR = 1000010;
const int MAXALFABET = 'z' - 'a' + 10;

int vf[MAXALFABET];
int max = -1,min = MAXALFABET;


void citire()
{
    char sir[MAXSIR];
    int l_sir = 0;
    freopen("ordine.in","r",stdin);
    freopen("ordine.out","w",stdout);
    gets(sir + 1);
    for (int i = 1;sir[i] != 0;++i)
    {
        ++l_sir;
        ++vf[sir[i] - 'a' + 1];
        if (sir[i] - 'a' + 1 > max)
            max = sir[i] - 'a' + 1;
        if (sir[i] - 'a' + 1 < min)
            min = sir[i] - 'a' + 1;
    }
}

void prelucrare()
{
    char sir[MAXSIR];
    int l_sir = 0;
    int poz_afisat = min;
    sir[++l_sir] = 'a' + min - 1;
    --vf[min];

    for (int i = 1;i <= l_sir;++i)
        for (int j = min;j <= max;++j)
            if (vf[j] != 0 && j != poz_afisat)
            {
                poz_afisat = j;
                sir[++l_sir] = 'a' + j - 1;
                --vf[j];
                break;
            }
    puts(sir + 1);
}

int main()
{
    citire();
    prelucrare();
    return 0;
}