Sum of Elements in an Even Indexed Array

Array

Given an array of integers, return the sum of the elements at even indices (i.e., indexes 0, 2, 4, ...).

Example 1

Input

[
  1,
  2,
  3,
  4,
  5,
  6
]

Output

Explanation. The sum of elements at even indices 0, 2, and 4 is 1 + 3 + 5 = 9.

Example 2

Input

Output

110010

Explanation. The sum of elements at even indices 0, 2, and 4 is 10 + 1000 + 100000 = 110010.

Example 3

Input

[
  -5,
  -5,
  -5,
  -5
]

Output

-10

Explanation. The sum of elements at even indices 0 and 2 is -5 + -5 = -10.

Follow-up: How would you optimize your solution if you know that the array could be very large, potentially containing up to 10 million integers?

Constraints:

The array will contain between 1 and 1000 elements, and each element will be an integer between -1000 to 1000.