#include<stdio.h>
#include<ctype.h>
#include<string.h>
int main(){
    char s[201];
    
    if(!fgets(s,sizeof s, stdin))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;
}