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 Haskell (GHC 8.8.3) (judge verdict: Accepted)

import qualified Data.ByteString.Char8 as C
import Data.Vector.Unboxed
import Prelude hiding (tail)

main = C.interact $ put . sol . get
get = unfoldr (C.readInt . C.dropWhile (<'0'))
put = C.pack . show
sol = ifoldl' (\s i a -> if even i then s-a+1 else s+a) 0 . tail