Kattis

# 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.

Sample Input 1 Sample Output 1
3
10 14
13 17
25 26

10

Sample Input 2 Sample Output 2
2
1 365
20 28

365

Sample Input 3 Sample Output 3
4
29 29
48 48
102 102
94 94

4