You are in charge of adding cheese topping to a pizza prepared for a special customer. This pizza is a very long rectangular strip. It is divided into $N$ slices, numbered $1$ to $N$ from left to right. To add cheese topping to the pizza, you have a special machine that can add $1$ unit of cheese on each slice in a consecutive group of slices (for example, you can add $1$ unit of cheese on each slice between slice $2$ and $4$ inclusive, adding a total of $3$ units of cheese). Each slice can carry an unlimited amount of cheese.

You plan to run the machine $R$ times, each time adding $1$ unit of cheese to each slice in a given range.

The customer is on a diet. When he eats the section of pizza from slice $x$ to slice $y$, inclusive, he would like to know how many units of cheese he is consuming.

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Input Specification

The first line will contain the integer $N$, the length of your long pizza.

The second line will consist of two space-separated integers $x$ and $y$, indicating that the customer is planning to eat every slice between slice $x$ and slice $y$ inclusive.

The third line will contain the integer $R$, the number of times you plan to run the topping machine.

The following $R$ lines will each describe one planned run of the topping machine using 2 space-separated integers, $l$ and $r$ $(l\le r)$, indicating that the machine will add $1$ unit of cheese onto each slice between slices $l$ and $r$, inclusive.

Output Specification

Please output the total number of units of cheese on all of the slices the customer is planning to eat.

Constraints and Partial Marks

For $4$ of the $10$ available marks, $R\le 1000$ and $N\le {10}^5$.

For the remaining $6$ marks, $R\le 4000$ and $N\le {10}^7$.

Sample Input

10
3 5
3
2 6
4 5
3 3

Sample Output

6

Explanation of Sample Output

After running the machine three times, the amount of cheese on each slice of pizza is as follows:

Slice #:  1  2  3  4  5  6  7  8  9  10
Cheese:   0  1  2  2  2  1  0  0  0  0

Therefore, slices $3$ to $5$ have a total of $6$ units of cheese.