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

count_1 = 0
rest = []

for c in s:
    if c in {'3', '5', '7'}:
        count_1 += 1
    else:
        rest.append(c)

count_2 = 0
i = 0
while i < len(rest) - 1:
    if (rest[i] == '1' and rest[i+1] == '1') or (rest[i] == '1' and rest[i+1] == '9'):
        count_2 += 1
        i += 2
    else:
        i += 1

print(count_1 + count_2)