Problem:
Score : 200 points

Problem Statement

Joisino is working as a receptionist at a theater.

The theater has 100000 seats, numbered from 1 to 100000.

According to her memo, N groups of audiences have come so far, and the i-th group occupies the consecutive seats from Seat l_i to Seat r_i (inclusive).

How many people are sitting at the theater now?

Constraints

1≤N≤1000

1≤l_i≤r_i≤100000

No seat is occupied by more than one person.

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
l_1 r_1
:
l_N r_N

Output

Print the number of people sitting at the theater.

Sample Input 1

1
24 30

Sample Output 1

7

There are 7 people, sitting at Seat 24,25,26,27,28,29 and 30.

Sample Input 2

2
6 8
3 3

Sample Output 2

4

Solution in Common Lisp (SBCL 2.0.3) (judge verdict: Accepted)

(defun read-list (x &optional ret)
  (if (< x 1)
    ret
    (read-list (1- x) (cons (read) (cons (read) ret)))))

(defun count-people (lst &optional (ans 0))
  (if (null lst)
    ans
    (count-people (cddr lst) (+ (1+ (- (cadr lst) (car lst))) ans))))

(let* ((n (read))
       (l (read-list n)))

  (format t "~A~%"
          (count-people l)))