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?

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.

Constraints

• 1≤N≤1000
• 1≤l_i≤r_i≤100000
• No seat is occupied by more than one person.
• All input values are integers.

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

见题面 Input 部分

见题面 Output 部分