import sys

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

def main():
    n = int(input())
    s = input()
    ans = 0
    c1 = c9 = 0
    flag = False
    for c in s:
        if c == "3" or c == "5" or c == "7": ans += 1
        if c == "1":
            c1 += 1
            if c9 > 1:
                flag = True
        if c == "9": c9 += 1
    ans += c1 // 2
    if c1 % 2 and flag:
        ans += 1
    print(ans)

main()