Uncle of Mr. Gentjan Bajrami has passed away leaving a great castle to his only cousin Mr. Bajrami. The castle is very large and has a lot of rooms. Mr. Bajrami wants to change the carpets in the rooms. He has measured and taken notes for the rooms and now he wants to see how many metre square of carpet he needs.

Write a program that is going to read the size of rooms and calculate the size of the carpet needed to buy.

Input specification
The first line has an integer number (n) which shows the number of rooms where 1 ≤ n ≤ 1000. The following n lines contain integer number pairs (width and depth), where 1 ≤ width, depth ≤ 20.

Output specification
Show one number that represent the size (in m²) of the carpet needed to buy.

Sample Input:
  3
  5 2
  4 3
  4 2


Sample Output:
  30

Output Explanation:
   Total size of the carpet = ((5 * 2) + (4 * 3) + (4 * 2)) = 30