#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main() {
    char s[105];
    if (fgets(s, sizeof(s), stdin) == NULL) {
        printf("Invalid input");
        return 0;
    }
    size_t len = strlen(s);
    if (len > 0 && s[len - 1] == '\n')
        s[len - 1] = '\0';
    
    int visited[256] = {0};
    char result[101];
    int k = 0;
    
    for (int i = 0; s[i] != '\0'; i++) {
        char c = s[i];
        if (!(isalpha(c) && c = ' ')) {
            printf("Invalid input");
            return 0;
        }
        if (c == ' ')
            continue;
        if (!visited[(unsigned char)c]) {
            visited[(unsigned char)c] = 1;
            result[k++] = c;
        }
    }
    
    result[k] = '\0';
    printf("%s", result);
    
    return 0;
}