n = int(input())
s = input().strip()

count_357 = 0
remaining = []
for c in s:
    if c in {'3', '5', '7'}:
        count_357 += 1
    else:
        remaining.append(c)

count_1 = 0
count_19 = 0
for c in remaining:
    if c == '1':
        count_1 += 1
    elif c == '9':
        if count_1 > 0:
            count_19 += 1
            count_1 -= 1

count_11 = count_1 // 2
total = count_357 + count_19 + count_11

print(total)