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

ans = 0
l = []
for i in S:
    if i == '1' or i == '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
nine -= count
if nine // 2 <= one:
    ans += nine // 2
    one -= nine // 2
else:
    ans += one
    one = 0
ans += one // 2
print(ans)