#include<stdio.h>
#include<ctype.h>
#include<string.h>
int main(){
    char s[101];
    int freq[256]={0};
    if(!fgets(s,sizeof(s),stdin))return 0;
    s[strcspn(s,"\n")]='\o';
    for(int i=0;s[i]!='\0';i++){
        unsigned char c=(unsigned char)s[i];
        if(!(isalnum(c)||c==' ')){
             printf("Invalid input\n");
             return 0;
        }
        freq[c]++;
    }
        char out[250];
        int j=0;
     for(int i=0;s[i]!='\0';i++){
        unsigned char c=(unsigned char)s[i];
        if(freq[c]==1)out[j++]=s[i];
}
out[j]='\0';
printf("%s",out);
return 0;
}