P9810 [CCC 2015 S1] Zero That Out

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. |$a_i$|Sequence| |:--:|:--:| |$1$|$\{1\}$| |$3$|$\{1,3\}$| |$5$|$\{1,3,5\}$| |$4$|$\{1,3,5,4\}$| |$0$|$\{1,3,5\}$| |$0$|$\{1,3\}$| |$7$|$\{1,3,7\}$| |$0$|$\{1,3\}$| |$0$|$\{1\}$| |$6$|$\{1,6\}$| You need to compute the sum of all numbers in the final sequence.

The first line contains an integer $k$. The next $k$ lines each contain an integer $a_i$.

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

**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