#include <stdio.h>
#include<string.h>
#include<ctype.h>
int main()
{
    char s[101];
    int freq[256]={0};
    int i;
    fgets(s,sizeof(s),stdin);
    s[strcspn(s,"\n")]='\0';
    for(i=0 ; s[i]!= '\0';i++);
    {
        if (!(isalpha(s[i]) || isdigit (s[i])||(s[i]==' '))
        {
            printf("Invalid input");
            return 0;
        }
    }
    
    for(i=0;s[i]!='\0';i++)
    {
        unsigned char c=s[i];
        freq[c]++;
    }
    
    for(i=0;s[i]!='\0';i++)
    {
        unsigned char c=s[i];
        if (freq[c]==1)
        printf("%c",c);
    }
    printf("\n");
    
}