#include <stdio.h>

int n;
int i, j, k;
int s[30];
char c;
int last;

int main()
{
    freopen("ordine.in", "r", stdin);
    freopen("ordine.out", "w", stdout);
    scanf("%c", &c);
    while ( 'a' <= c && c <= 'z' )
    {
        s[(int)(c-'a'+1)]++;
        n++;
        scanf("%c", &c);
    }
    
    for ( i = 1; i <= n; i++ )
        for ( j = 1; j <= 26; j++ )
            if ( s[j] && j != last )
            {
                printf("%c", (char)(j-1+'a'));
                last = j;
                s[j]--;
                break;
            }
    return 0;        
}