Score: $100$ points

问题陈述

有 $N$ 个人，编号为 $1$ 到 $N$，他们进行了几场一对一的比赛，没有平局。最初，每个人的得分都是 $0$。在每场比赛中，胜者的得分增加 $1$，而败者的得分减少 $1$（得分可以变成负数）。如果第 $i$ 个人的最终得分是 $A_i\ (1\leq i\leq N-1)$，请确定第 $N$ 个人的最终得分。可以证明，无论比赛的顺序如何，第 $N$ 个人的最终得分都是唯一确定的。

以上为大语言模型 kimi 翻译，仅供参考。

Problem Statement

There are $N$ people labeled $1$ to $N$, who have played several one-on-one games without draws. Initially, each person started with $0$ points. In each game, the winner's score increased by $1$ and the loser's score decreased by $1$ (scores can become negative). Determine the final score of person $N$ if the final score of person $i\ (1\leq i\leq N-1)$ is $A_i$. It can be shown that the final score of person $N$ is uniquely determined regardless of the sequence of games.

Constraints

• $2 \leq N \leq 100$
• $-100 \leq A_i \leq 100$
• All input values are integers.

Input

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

$N$

$A_1$ $A_2$ $\ldots$ $A_{N-1}$

Output

Print the answer.

Sample Input 1

4
1 -2 -1

Sample Output 1

2

Here is one possible sequence of games where the final scores of persons $1, 2, 3$ are $1, -2, -1$, respectively.

• Initially, persons $1, 2, 3, 4$ have $0, 0, 0, 0$ points, respectively.
• Persons $1$ and $2$ play, and person $1$ wins. The players now have $1, -1, 0, 0$ point(s).
• Persons $1$ and $4$ play, and person $4$ wins. The players now have $0, -1, 0, 1$ point(s).
• Persons $1$ and $2$ play, and person $1$ wins. The players now have $1, -2, 0, 1$ point(s).
• Persons $2$ and $3$ play, and person $2$ wins. The players now have $1, -1, -1, 1$ point(s).
• Persons $2$ and $4$ play, and person $4$ wins. The players now have $1, -2, -1, 2$ point(s).

In this case, the final score of person $4$ is $2$. Other possible sequences of games exist, but the score of person $4$ will always be $2$ regardless of the progression.

Sample Input 2

3
0 0

Sample Output 2

0

Sample Input 3

6
10 20 30 40 50

Sample Output 3

-150