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