#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main()
{
   char s[105];
   fgets(s,sizeof(s),stdin);
   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;
}