Virtual contest is a way to take part in past contest, as close as possible to participation on time. It is supported only ACM-ICPC mode for virtual contests.
If you've seen these problems, a virtual contest is not for you - solve these problems in the archive.
If you just want to solve some problem from a contest, a virtual contest is not for you - solve this problem in the archive.
Never use someone else's code, read the tutorials or communicate with other person during a virtual contest.

No tag edit access

M. Weather Tomorrow

time limit per test

1 secondmemory limit per test

256 megabytesinput

standard inputoutput

standard outputVasya came up with his own weather forecasting method. He knows the information about the average air temperature for each of the last *n* days. Assume that the average air temperature for each day is integral.

Vasya believes that if the average temperatures over the last *n* days form an arithmetic progression, where the first term equals to the average temperature on the first day, the second term equals to the average temperature on the second day and so on, then the average temperature of the next (*n* + 1)-th day will be equal to the next term of the arithmetic progression. Otherwise, according to Vasya's method, the temperature of the (*n* + 1)-th day will be equal to the temperature of the *n*-th day.

Your task is to help Vasya predict the average temperature for tomorrow, i. e. for the (*n* + 1)-th day.

Input

The first line contains a single integer *n* (2 ≤ *n* ≤ 100) — the number of days for which the average air temperature is known.

The second line contains a sequence of integers *t*_{1}, *t*_{2}, ..., *t*_{n} ( - 1000 ≤ *t*_{i} ≤ 1000) — where *t*_{i} is the average temperature in the *i*-th day.

Output

Print the average air temperature in the (*n* + 1)-th day, which Vasya predicts according to his method. Note that the absolute value of the predicted temperature can exceed 1000.

Examples

Input

5

10 5 0 -5 -10

Output

-15

Input

4

1 1 1 1

Output

1

Input

3

5 1 -5

Output

-5

Input

2

900 1000

Output

1100

Note

In the first example the sequence of the average temperatures is an arithmetic progression where the first term is 10 and each following terms decreases by 5. So the predicted average temperature for the sixth day is - 10 - 5 = - 15.

In the second example the sequence of the average temperatures is an arithmetic progression where the first term is 1 and each following terms equals to the previous one. So the predicted average temperature in the fifth day is 1.

In the third example the average temperatures do not form an arithmetic progression, so the average temperature of the fourth day equals to the temperature of the third day and equals to - 5.

In the fourth example the sequence of the average temperatures is an arithmetic progression where the first term is 900 and each the following terms increase by 100. So predicted average temperature in the third day is 1000 + 100 = 1100.

Codeforces (c) Copyright 2010-2017 Mike Mirzayanov

The only programming contests Web 2.0 platform

Server time: Oct/17/2017 07:10:55 (c4).

Desktop version, switch to mobile version.

User lists

Name |
---|