INF = 1<<32
N = int(input())
A = list(map(int,input().split()))
S = sum(A)
ans = INF
for M in range(1,N+1,2):
    P = [0] * M
    cnt = 1
    for i in range(M//2):
        P[i] = cnt
        cnt += 1
    for i in range(M//2,M):
        P[i] = cnt
        cnt -= 1
    for k in range(N-M+1):
        ret = S
        cnt = S
        for i in range(M):
            ret -= A[i+k]
            cnt -= A[i+k]
            if A[i+k] > P[i]:
                ret += A[i+k] - P[i]
                cnt += A[i+k] - P[i]
            if A[i+k] < P[i]:
                cnt -= P[i] - A[i+k]
        if cnt < 0:
            ret += INF
        ans = min(ans, ret)
print(ans)