#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[200];
    int freq[256]={0};
    int fgets(s,sizeof(s),stdin))return 0;
    s[strcspn(s,"\n")]='\0';
    for(int i= 0;s[i]!='\0';i++){
        unsigned char c=(unsigned char)s[i];
        if(!(isalnum(c)||c==' '))
        {
            printf("Invalid input");
            return 0;
        }
        freq[c]++;
   }
   char out[205];
   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;
}