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.

Constraints

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

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.