Contacts#2797
My mobile phone is configured so that after any call, if the phone number is not already in the contact book, it is automatically added. Given a list of phone numbers from all mobile connections, determine how many unique entries are in the contact book.
The first line contains the integer (1 \le N \le 10^5). The second line contains phone numbers, each a nine-digit natural number.
Print the number of unique entries in the contact book.
Example 1