0723. Very Easy!!!

Time limit : 1000 ms Memory limit : 64 mb

You are given the value of n and a. Determine the answer for the following series:

Input

Two positive integers n and a.

Output

Print the value of sum. It is known that the result is no more than 2*1018.

Samples

 № Input Output 1 3 3 102 2 4 4 1252