Problem Statement

We have a blackboard with nothing written on it.
Takahashi will do N operations to write integers on it.
In the i-th operation, he will write each integer from A_i through B_i once, for a total of B_i - A_i + 1 integers.
Find the sum of the integers written on the blackboard after the N operations.

Input

Input is given from Standard Input in the following format:
N
A_1 B_1
$\vdots$
A_N B_N

Output

Print the sum of the integers written on the blackboard after the N operations.

Constraints

• All values in input are integers.
• $1 \leq N \leq 10^5$
• $1 \leq A_i \leq B_i \leq 10^6$

Sample Input 1

2
1 3
3 5

Sample Output 1

18

In the 1-st operation, he will write 1, 2, and 3 on the blackboard.
In the 2-nd operation, he will write 3, 4, and 5 on the blackboard.
The sum of the integers written is 1+2+3+3+4+5=18.

Sample Input 2

3
11 13
17 47
359 44683

Sample Output 2

998244353

Sample Input 3

1
1 1000000

Sample Output 3

500000500000

见题面 Input 部分

见题面 Output 部分