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

LANS=1<<60

def calc(A,k):
    
    ANS=0
    X=[min(i+1,k-i) for i in range(k)]
    #print(X)

    while len(X)<N:
        X.append(0)

    for i in range(N):
        while A[i]>X[i]:
            ANS+=1
            A[i]-=1
            for j in range(N):
                if A[j]<X[j]:
                    A[j]+=1
                    break
    if X==A:
        return ANS
    else:
        return 1<<60

for i in range(1,N+1,2):
    LANS=min(LANS,calc(A[:],i))

print(LANS)