Problem Statement

You are given an integer sequence of length $N$: $A=(A_1,A_2,\dots,A_N)$. Find the sum of the odd-indexed terms of $A$. More formally, find the sum of $A_i$ over all odd $i$ satisfying $1 \le i \le N$.

Constraints

• All input values are integers.
• $1 \le N \le 100$
• $1 \le A_i \le 100$

Input

The input is given from Standard Input in the following format:

• $N$
• $A_1$ $A_2$ $\ldots$ $A_N$

Output

Output the answer.

5
3 1 4 1 5

12

In this input, $A=(3,1,4,1,5)$, and the terms to be summed are $A_1,A_3,A_5$. Output their sum, that is, $3+4+5=12$.

6
2 7 1 8 2 8

5

In this input, $A=(2,7,1,8,2,8)$, and the terms to be summed are $A_1,A_3,A_5$. Output their sum, that is, $2+1+2=5$.

9
100 40 30 50 20 90 100 80 60

310

• Source: AtCoder ABC 479 A