#include<stdio.h>
#include<ctype.h>
int main(){
    char s[101],out[101];
    int used[256]={0},i,j=0;
        fgets(s,101,stdin);
        for(i=0;s[i];i++){
            if(!(isalnum(s[i]) || s[i] ==' ')){
                printf("Invalid input");
                return 0;
            }
        }
        for(i=0;s[i];i++){
            if(!used[(unsigned char)s[i]]){
                out[j++]=s[i];
                used[(unsigned char)s[i]]=1;
            }
        }
        out[j]=''
    }