INF = 1<<32
M = 200
N = int(input())
A = list(map(int,input().split()))
ans = INF
for X in range(M):
    for Len in range(1,M,2):
        if X + Len > M:
            break
        P = [0] * M
        cnt = 1
        Mid = Len // 2
        for i in range(Len):
            P[X+i] = cnt
            if i < Mid:
                cnt += 1
            else:
                cnt -= 1
        for Y in range(M):
            if Y + N > M:
                break
            Q = [0] * M
            for i in range(N):
                Q[Y+i] = A[i]
            ret = 0
            cnt = 0
            for i in range(M):
                if P[i] < Q[i]:
                    ret += Q[i] - P[i]
                    cnt += Q[i] - P[i]
                else:
                    cnt -= P[i] - Q[i]
            if cnt < 0:
                ret += INF
            ans = min(ans, ret)
print(ans)