N = int(raw_input())
A = map(int,raw_input().split())
ans = 1e10
for n in range(1,10001,2):
    P = [min(i,n+1-i) for i in range(1,n+1)]
    if sum(P) > sum(A): break
    for j in range(N-len(P)+1):
        over = lack = 0
        for k in range(n):
            tmp = A[j+k]-P[k]
            over += max(0,tmp)
            lack += abs(min(0,tmp))
        ans = min(ans, max(over,lack)+max(0,sum(A)-sum(P)-abs(over-lack)))
print ans