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-i]:
        ans += 1
    else:
        one = one[i:]
        nine = nine[:len(nine)-i]
        break

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