Fill the line

Very easy

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

$n$ segments are painted on the line. The coordinates of the left and right ends of each segment $l_{i}$ and $r_{i}$ are known. Find the length of the colored part of the line.

Input

The first line contains the number $n (1 \leq n \leq 15000)$ , the following $n$ lines contains the pair of integers $l_{i}$ and $r_{i} (- 1 0^{9} \leq l_{i} \leq r_{i} \leq 1 0^{9})$ .

Output

Print the length of the colored part of the line.

Examples

Input #1

Answer #1

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