Problem Description

Given $k$ integers $a_1, a_2 \dots, a_k$, maintain a sequence and perform the following operations in order:

• When $a_i = 0$, delete the last number that was added to the sequence.
• Otherwise, add $a_i$ to the sequence.

For example, when $a = \{1,3,5,4,0,0,7,0,0,6\}$, the operations are as follows.

You need to compute the sum of all numbers in the final sequence.

Input Format

The first line contains an integer $k$.

The next $k$ lines each contain an integer $a_i$.

Output Format

Output one line with one integer, representing the sum of all numbers in the final sequence.

4
3
0
4
0

0

10
1
3
5
4
0
0
7
0
0
6

7

Hint

Constraints:

$1 \le k \le 10^5$, $0 \le a_i \le 100$.

It is guaranteed that when $a_i = 0$, the sequence is not empty.

Translated by ChatGPT 5