n = int(input())
aa = list(map(int,input().split()))

n+=100
aa+=[0]*100

aasum = sum(aa)

result = aasum
for l in range(n-1):
    for r in range(l,n):
        if (r-l)%2: continue
        bb = [0]*n
        for x in range(l,r+1):
            bb[x] = min(x-l,r-x)+1
        if sum(bb) > aasum: continue
        s = 0
        for x in range(n):
            s+= max(0,aa[x]-bb[x]) # 減らす方のみカウント
        result = min(result,s)

print(result)