N = int(input())
lsA = list(map(int,input().split()))+[0]*(200)
sa = sum(lsA)
ans = float('INF')
for j in range(1,200,2):#可能性があるのが100個
    pr = [min(i+1,j-i) for i in range(j)]+[0]*(200)
    sm = sum(pr)
    if sm > sa:
        continue
    #削る数
    cnt1 = 0
    for i in range(max(N,j)):
        cnt1 += max(0,lsA[i]-pr[i])
    ans = min(ans,cnt1)
print(ans)