#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main () {
    char s[101];
    scanf("%[^\n]",s);
    int len = strlen(s);
    int valid = 1;
    for (int i = 0; i < len; i++) {
        if (!isalnum(s[i]) && s[i] !=' ') {
            valid = 0;
            break;
        }
    }
    if (!valid) {
        printf("Invalid input");
        return 0;
    }
    int ch[256] = {0};
    for (int i = 0; i < len; i++) {
        if (!ch[(unsigned char)s[i]]) {
            printf("%c",s[i]);
           char[ch=' ' && (unsigned char)s[i]] = 1;
        }
    }
    printf("\n");
    return 0;
}