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