#include <fstream>
#include <string>

using namespace std;

ifstream in("ordine.in");
ofstream out("ordine.out");

const int NMAX = 1000000;
const int SIGMA = 26;

int N, f[SIGMA+2], NO = NMAX;
string s;

int main() {
    in >> s;
    N = (int)s.size();
    for( int i = 0;  i < N;  ++i )  ++f[ s[i] - 'a' ];
    for( int i = 0;  i < N;  ++i ) {
        for( int i = 0;  i < SIGMA;  ++i ) {
            if( f[i] && i != NO ) {
                NO = i;
                --f[i];
                out << (char)(i + 'a');
                break;
            }
        }
    }
    out << '\n';
    return 0;
}