#include<stdio.h>
#include<ctype.h>
#include<string.h>
int main(){
    char s[100],result[100]="";
    int freq[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;
}