n = int(input())
S = input()
one = []
nine = []
ans = 0
add = 0
for i,s in enumerate(S):
    if s == "1":
        one.append(i)
    elif s == "9":
        if len(one) > add:
            add += 1
            ans += 1
        else:
            nine.append(i)
    else:
        ans += 1
one = one[add:]
ans += min(len(nine)//2,len(one)) + max(0,(len(one)-len(nine)//2))//2
print(ans)