Wayne is playing video games. While playing, they grind ~N~ different kinds of enemies. Each enemy drops ~a_i~ experience and they defeat ~b_i~ of each. How much experience did Wayne get?

Limitations

~1 \le N \le 100~
~1 \le a_i, b_i \le 2000~

Sample Input

2
5 4
8 2

Sample Output

36

Sample Explanation

Wayne fought 4 of the 1st enemy, getting ~5 + 5 + 5 + 5 = 20~ xp.
Then they fought 2 of the 2nd enemy, getting ~8 + 8 = 16~ xp.
In total, they gained 36 xp.