Draw!

Description:

Input:

The first line contains a single integer $$$n$$$ ($$$1 \le n \le 10000$$$) — the number of known moments in the match.

Each of the next $$$n$$$ lines contains integers $$$a_i$$$ and $$$b_i$$$ ($$$0 \le a_i, b_i \le 10^9$$$), denoting the score of the match at that moment (that is, the number of goals by the first team and the number of goals by the second team).

All moments are given in chronological order, that is, sequences $$$x_i$$$ and $$$y_j$$$ are non-decreasing. The last score denotes the final result of the match.

Output:

Print the maximum number of moments of time, during which the score was a draw. The starting moment of the match (with a score 0:0) is also counted.

Sample Input:

3
2 0
3 1
3 4

Sample Output:

2

Sample Input:

3
0 0
0 0
0 0

Sample Output:

1

Sample Input:

1
5 4

Sample Output:

5

Note:

In the example one of the possible score sequences leading to the maximum number of draws is as follows: 0:0, 1:0, 2:0, 2:1, 3:1, 3:2, 3:3, 3:4.