Subscriber Roster Duplicate Sweep

A newsletter's signup form logs every submission as a brand-new record, each tagged with a unique record id and the email address that was entered. Because visitors could resubmit the form (for example, after a network hiccup), some email addresses end up appearing in multiple records even though the form assigns a fresh id to every submission. Given the raw signup log, find every email address that appears in two or more records.

Input format

• Line 1: a single integer n, the number of signup records.
• Each of the next n lines contains one record: an integer id_i followed by a single space and an email address string email_i (no embedded whitespace).

Output format

• First line: an integer k, the number of distinct email addresses that appear in two or more records.
• Next k lines: each such duplicated email address, printed in lexicographically ascending order, one per line. If k = 0, print only the first line (a single "0") and no further lines.

Constraints

• 1 <= n <= 100000
• 1 <= id_i <= 10^9, and all id_i are distinct.
• Each email_i has length between 3 and 100 characters, contains no whitespace, and comparisons are case-sensitive (two emails that differ only in letter case are treated as different addresses).

5
1 a@x.com
2 b@x.com
3 a@x.com
4 c@x.com
5 b@x.com

2
a@x.com
b@x.com

3
10 alice@mail.com
20 bob@mail.com
30 carol@mail.com

0