## LCC '18 Contest 4 J1 - Terminus Quest

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Points: 3 (partial)
Time limit: 2.0s
Memory limit: 64M

Author:
Problem type

On his quest to solve Terminus Est, Max finds an ancient scroll that claims to be the key to solving the problem.

The scroll proclaims:

The one to solve Terminus Est shall be able to recognize patterns.

Max interprets this as the ability to recognize arithmetic patterns.

Max defines an arithmetic pattern as a list ($$a$$) of $$N$$ integers where the difference between any adjacent pair is the same.

The difference of an adjacent pair of integers is defined as $$a_i - a_{i - 1}$$ for all $$i$$, $$2 \le i \le N$$.

Can you determine if a list of numbers is an arithmetic pattern?

#### Input Specification

The first line contains a single integer, $$N$$. $$2 \leq N \leq 1000$$.

The next line describes the list of numbers by providing $$N$$ space separated integers where the $$i$$th integer describes $$a_i$$. $$0 \leq a_i \leq 10^6$$

#### Output Specification

YES if the input list is an arithmetic pattern. NO if the input list is not an arithmetic pattern.

#### Sample Input

5
2 4 6 8 10

#### Sample Output

YES