Polynomial Derivative (Small)

Given the nonzero terms of a polynomial, compute the value of its derivative at x = 1.

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Description

Examples2

Problem

Seongmin is taking calculus this semester. While working through the homework on differentiating polynomials, he got tired of doing it by hand, so he decided to write a program that takes a function $f(x)$ and returns its derivative $f'(x)$ for him.

You are given the coefficient and the degree of every term of a polynomial $f(x)$ . Compute $f'(1)$ .

Input

The first line contains the number of terms N (1 ≤ N ≤ 100).

Each of the next N lines contains the coefficient C (-100 ≤ C ≤ 100, C ≠ 0) and the degree K (0 ≤ K ≤ 1000) of one term, separated by a space. The terms are given in decreasing order of degree, and no degree appears more than once.

Output

Print the value of $f'(1)$ on the first line.

Hint

Differentiating $f(x) = 3x^3 + 2x^2 + x$ gives $f'(x) = 9x^2 + 4x + 1$ .

So $f'(1) = 9 + 4 + 1 = 14$ .