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

count_singles = 0
remaining = []

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

unpaired_1 = 0
count_pairs = 0

for c in remaining:
    if c == '1':
        if unpaired_1 > 0:
            count_pairs += 1
            unpaired_1 = 0
        else:
            unpaired_1 += 1
    elif c == '9':
        if unpaired_1 > 0:
            count_pairs += 1
            unpaired_1 = 0

total = count_singles + count_pairs
print(total)