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)

n=int(input())
a=list(map(int,input().split()))

total = sum(a)
oneTri = n*(n+1)//2
if total%oneTri!=0:
    print("NO")
    exit()

trial = total//oneTri

cnt=0
for i in range(n):
    sa = a[i-1] + trial - a[i]
    if sa == 0:
        continue
    if sa % n != 0 or sa < 0:
        print("NO")
        exit()
    cnt += sa//n

if cnt != trial:
    print("NO")
else:
    print("YES")