#include <fstream>
#include <cstring>
using namespace std;
ifstream fin("ordine.in");
ofstream fout("ordine.out");
char s[1000005],x,y;
int i,a[30],n,j;
int main()
{fin>>s;
 n=strlen(s);
 for(i=0;i<n;++i)
    {a[s[i]-96]++;
    }
    n=strlen(s);
 for(i=0;i<n;++i)
    {for(j=1;j<=26;j++)
        {x=j+96;
         if(a[j]>0&&y!=x){a[j]--;y=x;fout<<x;break;}
        }
    }

}