#include <stdio.h>
#include <string.h>
#include <ctype.h>
int isValidchar(char c)
{
    return (isalpha(c)|| isdigit(c)||isspace(c));
}
int main() 
{
    char str[101];
    int seen[256] = {0};
    int i, len;
    fgets(str, sizeof(str), stdin);
    len = strlen(str);
    if (len > 0 && str[len - 1] == '\n')
    {
        str[len - 1] = '\0';
    }
    for (i = 0; str[i] != '\0'; i++)
    {
        if (!isValidChar(str[i])) 
        {
            printf("Invalid input");
            return 0;
        }
    } 
    for (i = 0; str[i] !='\0'; i++)
    {
        if(!seen[(unsigned char)str[i]])
        {
            printf("%c",str[i]);seen[(unsigned char)str[i]] = 1;
        }
    }
    return 0;
}