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

 int main(){
     char s[105];
     fgets(s,sizeof(s),stdlin);
     int n=strlen(s);
     
     if(s[n-1]==:\n){
         s[n -1]='\0';
         n--;
     }
     int seen[256]={0};
     char result[105];
     int k=0;
     
     for(int i =0;i<n;i++){
         char c=s[i];
         
         if (!(isalnum(c)|| c=='')){
             printf("Invalid input");
             return 0;
         }
         if (!seen[(unsigned char)c]){
             result[k++]=c;
             seen[(unsigned char)c]=1;
         }
     }
     result[k]='\0';
     printf("%s",result);
     
     return 0;
 }