#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main()
{
    char s[101];
    int count[256] = {0};
    scanf(" %[^\n]", s);
    for (int i = 0; s[i] != '\0'; i++){
        char ch = s[i];
        if (!((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z') || (ch >= '0' && ch <= '9')))
        {
            
         printf("Invalid input\n");
          return 0;
        }
        count[(unsigned char)ch]++;
    }
    for (int i = 0; s[i] != '\0'; i++){
        char ch = s[i];
        if (ch !==' ' &&count[(unsigned char)ch] == 1)
        {
            printf("%c", ch);
        }
    }
    printf("\n");
    return 0;
}