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