## 26 May Friday 17:00 Python Practice 21.05.21.

**Question:**

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

*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.*

**N**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

*, inclusive, he would like to know how many units of cheese he is consuming.*

**y****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

*and slice*

**x***inclusive.*

**y**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,

**and**

*l***(**

*r**≤*

**l****), indicating that the machine will add 1 unit of cheese onto each slice between slices**

*r**and*

**l****, inclusive.**

*r***Output Specification**

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

Sample Input

10

3 5

3

2 6

4 5

3 3Sample Output

6Explanation 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 3−5 have a total of 6 units of cheese.

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