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

int main() {
    char s[201];
    if(!gets(s,sizeof s,studin))return 0;
    int n=strlen(s);
    if(n>0 && s[n-1] == '\n'){s[n-1]='\0';n--;}
    int freq[256]={0};
    for(int i=0;i<n;++i){
        unsigned char c=(unsigned char)s[i];
        if(!(isalnum(c) || c==' ')){
            printf("Invalid input");
            return 0;
        }
        freq[c]++;
    }
    for(int i=0;i<n;i++){
        unsigned char c=(unsigned char)s[i];
        if(freq[c] == 1)putchar(c);
    }
    return 0;
}