#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
N = int(readline())
S = read().rstrip().decode()

# %%
S = S.replace('3', '')
S = S.replace('5', '')
S = S.replace('7', '')
answer = N - len(S)

# %%
T = [0]
for x in map(int, S):
    if x == 9 and T[-1] == 1:
        answer += 1
        T.pop()
    else:
        T.append(x)

x9 = T.count(9)
x1 = T.count(1)
n = min(x9 // 2, x1)
answer += n
x1 -= n
answer += x1 // 2
print(answer)