#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;
}
}