N = int(input())
S = input()

ans = 0
l = []
for i in S:
    if i == '1' or '9':
        l.append(i)
    else:
        ans += 1
one = 0
nine = 0
now = 0
count = 0
for i in l:
    if i == "1":
        now += 1
        one += 1
    else:
        nine += 1
        if now > 0:
            count += 1
            now -= 1
ans += count + (one - count) // 2
if onw - count == 1 and nine - count >= 2:
    ans += 1
print(ans)