Next-Day Contact Retention Rate

Mission control keeps a contact log for a fleet of satellites: each entry records a satellite's id and the calendar day (a plain integer day number counted from an arbitrary epoch) on which mission control received a signal from it. For every distinct satellite in the log, its first-contact day is the smallest day number recorded for it. A satellite is said to have a solid first link if mission control also received at least one signal from that same satellite on the very next calendar day (first-contact day + 1). Across all distinct satellites appearing in the log, compute the fraction that have a solid first link, rounded to exactly two decimal places.

Input format

• Line 1: one integer m — the number of log entries.
• Each of the next m lines contains two integers satellite_id day, meaning mission control received a signal from that satellite on that day. Entries are not guaranteed to be sorted by day, and the same (satellite_id, day) pair may appear more than once.

Output format

Print one line containing a single number: the count of satellites with a solid first link divided by the total count of distinct satellites in the log, rounded to exactly two decimal places (for example 0.33, 1.00, or 0.67).

Constraints

• 1 <= m <= 100000
• 0 <= satellite_id <= 100000
• 0 <= day <= 100000
• At least one distinct satellite id appears in the log.

5
1 10
1 11
2 50
3 11
3 90

0.33

5
1 1
1 1
1 2
2 5
2 6

1.00