Problem:
Score : 500 points

Problem Statement

There are N boxes arranged in a circle. The i-th box contains A_i stones.

Determine whether it is possible to remove all the stones from the boxes by repeatedly performing the following operation:

Select one box. Let the box be the i-th box. Then, for each j from 1 through N, remove exactly j stones from the (i+j)-th box. Here, the (N+k)-th box is identified with the k-th box.

Note that the operation cannot be performed if there is a box that does not contain enough number of stones to be removed.

Constraints

1 ≦ N ≦ 10^5

1 ≦ A_i ≦ 10^9

Input

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

N
A_1 A_2 … A_N

Output

If it is possible to remove all the stones from the boxes, print YES. Otherwise, print NO.

Sample Input 1

5
4 5 1 2 3

Sample Output 1

YES

All the stones can be removed in one operation by selecting the second box.

Sample Input 2

5
6 9 12 10 8

Sample Output 2

YES

Sample Input 3

4
1 2 3 1

Sample Output 3

NO

Solution in Python (3.4.3) (judge verdict: Accepted)

def main():
    N = int(input())
    A = list(map(int, input().split()))

    Asum = sum(A)
    rem = N * (N + 1) // 2
    if Asum % rem != 0:
        return False

    K = Asum // rem
    A.append(A[0])
    dif = [r - l for l, r in zip(A[:-1], A[1:])]
    for d in dif:
        if d > K:
            return False
        if (K - d) % N != 0:
            return False
    return True


if __name__ == "__main__":
    if main():
        print("YES")
    else:
        print("NO")