from collections import deque
n = int(input())
s = input()
li = []
ans = 0
for i in range(n):
    if s[i] != "1" and s[i] != "9":
        ans += 1
    else:
        li.append(s[i])

idx = set()
d1 = deque()
#d9 = deque()

for i in range(len(li)):
    if li[i] == "1":
        d1.append(i)
    if li[i] == "9":
        if len(d1) > 0:
            tmp = d1.popleft()
            idx.add(tmp)
            idx.add(i)
            ans += 1
        
li2 = []
for i in range(len(li)):
    if i not in idx:
        li2.append(li[i])
#print(li2,ans,len(li2))
#exit()

n9 = 0
n1 = 0
for i in range(len(li2)):
    if li2[i] == "1":
        n9 = i
        n1 = len(li2)-i
        break

tmp = min(n9//2,n1)
ans += tmp
ans += (n1-tmp)//2
print(ans)