Description

Given the start and end of each burning segment, please compute the total length of the burning positions.

Input Format

The first line contains an integer $n$, indicating the number of fire reports.
Then follow $n$ lines; each line contains two integers $a, b$, denoting the start and end of a burning segment (Note: left-closed, right-open).

Output Format

Output a single line with one integer representing the answer.

3
-1 1
5 11
2 9

11

Hint

Constraints

For all test points, it is guaranteed that $1 \leq n \leq 2 \times 10^4$, $-2^{31} \leq a < b \lt 2^{31}$, and the answer is less than $2^{31}$.

Translated by ChatGPT 5