#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char str[101];
    scanf ("%100[^\n]",str );
    int seen [256]={0};
    char result [101];
    int idx =0;
    for (int i=0;str[i]!='\0';i++)
    {
        char ch =str [i];
        if (!isalnum(ch) && ch !=''){
            printf ("invalid input ");
            return 0;
        }
        if (!seen[(unsigned char)ch]){
            
            result [idx++ ]=ch;
            seen[(unsigned char)ch]=1;
        }
        result[idx]='\0';
        printf("%s",result);
        
    }
    return 0;
}