# problem 1
N = int(input())
S = list(input())
ans = 0
dic = {"1": 0, "3": 0, "5": 0, "7": 0, "9": 0}
for some in S:
    dic[some] += 1

ans = dic["3"]+dic["5"]+dic["7"]
new = {1: 0, 9: 0}
for x in S:
    n = int(x)
    if n == 1: new[1] += 1
    if n == 9:
        new[9] += 1
        if new[1] > 0:
            new[1] -= 1
            new[9] -= 1
            ans += 1

if new[9] >= new[1]*2:
    ans += new[1]
    print(ans)
    exit()
    
elif new[9] < new[1]*2:

    if new[9]>1:
        p = new[9]//2
        ans += p
        new[1] -= p
        ans += new[1]//2
        print(ans)
        exit()
    else:
        print(ans)