n = int(input())
S = input()
one = []
nine = []
ans = 0
for i,s in enumerate(S):
    if s == "1":
        one.append(i)
    elif s == "9":
        nine.append(i)
    else:
        ans += 1

for i in range(min(len(one),len(nine))):
    if one[i] < nine[-1]:
        ans += 1
        nine.pop()
    else:
        one = one[i:]
        break

for i in range(min(len(one),len(nine)//2)):
    if nine[2*i+1] < one[-1]:
        ans += 1
        one.pop()
    else:
        break
ans += len(one)//2
print(ans)