#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main() {
    char s[105], result[105];
    int sfreq[256] = {0};
    int i,j = 0;

    if(!fgets(s, sizeof(s), stdin)){
        return 0;
    }
    s[strcspn(s, "\n")]='\0';

    for (int i = 0; s[i] != '\0'; i++) {
       
        if (!(isalnum((unsigned char)s[i]) || s[i]==' ')){  
            printf("Invalid input\n");
            return 0;
        }
    }
    for ( i = 0; s[i] != '\0'; i++) {
        unsigned char c=s[i];
         unsigned char check=  isalpha (c) ? tolower(c) : c;
         freq[check]++;
    }
        for ( i = 0; s[i] != '\0'; i++) {
        unsigned char c=s[i];
         unsigned char check=  isalpha (c) ? tolower(c) : c;
          if (freq[check]==1)
          {
             result[j++]=c; 
          
         }
    }

    result[j] = '\0';
    printf("%s\n", result);

    return 0;
}