#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;
}