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.

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.

Constraints

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

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

见题面 Input 部分

见题面 Output 部分