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

int main() {
    char str[105];
    fgets(str, sizeof(str), stdin); 
    
    int len = strlen(str);
    if (str[len - 1] == '\n') {
        str[len - 1] = '\0';  
        len--;
    }
     for (int i =0; i< len; i++)
     {
         if(!(isalnum(str[i] || str[i] == ' ')){
             printf("Invalid input \n");
             return 0;
         }
     }
        int freq[256] = {0};  
    for (int i = 0; i < len; i++)
    {
        unsigned char c = str[i];
        freq[c]++;
    }

    for (int i = 0; i < len; i++) {
        unsigned char c= str[i];
        if (freq[c] == 1) {
            printf("%c",c);

        }
    }
    printf("\n");

    return 0;
}