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