Mr. Alban Shehu runs GSS "Gezer Shoe Store". He wants to prepare a program for his invoices to calculate the total price.

Input specification
There are at least 1 and at most 10000 lines of input ending with a negative number. There are two integer numbers in every line: unitPrice and n.
    where unitPrice is the unit price of the given shoe type and it's 1 ≤ price ≤ 100
    n is the number of shoe pairs for this type and 1 ≤ n ≤ 1000.
The entry ends with a negative number .

Output specification
You will calculate and give one number: the sum of the invoice

Sample Input:
3 5
2 6
-1

Sample Output:
27