#!/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)

# %%
N = len(S)
S = S.replace('19', '')
answer += (N - len(S)) // 2

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