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 OCaml (4.02.3) (judge verdict: Accepted)

let () =
  let n = Scanf.scanf "%d\n" (fun n -> n) in
  let lrs = Array.init n (fun _ -> Scanf.scanf "%d %d\n" (fun l r -> l, r)) in
  Array.fold_left (fun a (l, r) -> a + r - l + 1) 0 lrs
  |> Printf.printf "%d\n"