Problem D
Free Food

Do you know what attracts almost any college student to participate in an event? Yes, free food. It doesn’t matter whether the event involves a long (sometimes boring) seminar. As long as free food is served for the event, then students will surely come.

Suppose there are $N$ events to be held this year. The $i^\textrm {th}$ event is scheduled from day $s_ i$ to day $t_ i$, and free food is served for that event every day from day $s_ i$ to day $t_ i$ (inclusive). Your task in this problem is to find out how many days there are in which free food is served by at least one event.

For example, let there be $N = 3$ events. The first event is held from day $10$ to $14$, the second event is held from day $13$ to $17$, and the third event is held from day $25$ to $26$. The days in which free food is served by at least one event are $10, 11, 12, 13, 14, 15, 16, 17, 25, 26$, for a total of $10$ days. Note that both events serve free food on days $13$ and $14$.

Input

The first line contains an integer $N$ ($1 \le N \le 100$) denoting the number of events. Each of the next $N$ lines contains two integers $s_ i$ and $t_ i$ ($1 \le s_ i \le t_ i \le 365$) denoting that the $i^\textrm {th}$ event will be held from $s_ i$ to $t_ i$ (inclusive), and free food is served for all of those days.

Output

The output contains an integer denoting the number of days in which free food is served by at least one event.

3
10 14
13 17
25 26

10

2
1 365
20 28

365

4
29 29
48 48
102 102
94 94

4