False Alarm

Faina is going to sleep, but she needs to wake up early tomorrow for a very important contest. She has already set $n$ alarms at different times between 7:00 and 9:00 in the morning.

However, Faina is a deep sleeper. To wake up, she needs to hear at least three alarms within a 10-minute span. In other words, for some three alarms, the difference between the first and the last alarm must be 10 minutes or less.

Faina is not sure whether her current alarms meet this condition, and she worries she might oversleep the contest and anger her teammates. So she wants to set some additional alarms. All new alarms must also be set between 7:00 and 9:00, and all alarms, including the old ones, must be at different times.

Find the smallest number of additional alarms Faina has to set to be confident that she will wake up. If she is already sure to wake up, the answer is $0$.

The first line contains a single integer $n$, the number of alarms Faina has set ($1 \le n \le 20$).

The $i$-th of the following $n$ lines contains the time of the $i$-th alarm in the h:mm format ($7 \le h \le 9$; $00 \le mm \le 59$; if $h = 9$, then $mm = 00$). The alarms are given in strictly increasing order of time.

Print the smallest number of additional alarms Faina has to set to guarantee that she wakes up.

In the first test, the three alarms at 7:56, 7:59, and 8:05 guarantee that Faina will wake up.

In the second test, any time between 8:00 and 9:00 that does not coincide with an existing alarm works.

In the third test, one possible solution is to set two more alarms at 7:45 and 7:46.