import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1

def main():
    n = int(input())
    s = input()
    ans = 0
    c1 = c9 = 0
    for c in s:
        if c == "1":
            if c9 > 1:
                c9 -= 2
                ans += 1
            else:
                c1 += 1
        elif c == "9":
            c9 += 1
        else:
            ans += 1
    ans += c1 // 2
    print(ans)

main()