#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main()
{
    char str[105];
    if(fgets(str, sizeof(str),stdin)==NULL){
        printf("Invalid input");
        return 0;
        
    }
    int len = strlen(str);
    if(str[len - 1] =='\n')str[len - 1]='\0';
    for(int i = 0; str[i] !='\0'; i++){
        if(!(isalnum(str[i]) && str[i]!='')){
            printf("Invalid input");
            return 0;
            
        }
    }
    int seen[256]={0};
    for(int i =0;str[i]!='\0';i++){
        if(!seen[(unsigned char)str[i]]){
            printf("%c",str[i]);
            seen[(unsigned char)str[i]]=1;
        }
    }
    return 0;
}