Position-Weighted Sum

Source: Phước Hưng OJ

Version: Phuoc Hung OJ Extended

Problem

Given $a_0,a_1,\ldots,a_{n-1}$, compute the 1-based position-weighted sum

Use a 64-bit accumulator.

Input

The first line contains $n$. The second line contains $n$ integers $a_i$.

Output

Print $S$.

Subtask

Subtask 1 (20 points): $1\le n\le10$, $|a_i|\le10^3$.

Subtask 2 (30 points): $1\le n\le1000$, $|a_i|\le10^6$.

Subtask 3 (50 points): $1\le n\le10^5$, $|a_i|\le10^9$.

Example

Input

4
3 -2 5 1

Output

18

Explanation

The result follows directly from the mathematical definition above.