#!/usr/bin/env python3
n = int(input())
s = input()
s = ''.join(s.split('3'))
s = ''.join(s.split('7'))
ans = n - len(s)
one = 0
nine = 0
nine_one = 0
for i in range(len(s))[::-1]:
    if s[i] == '9':
        if nine_one > 0:
            nine_one -= 1
            one -= 1
            ans += 1
        elif one > 0:
            nine_one += 1
            nine += 1
        else:
            nine += 1
    if s[i] == '1':
        if one > 0:
            one -= 1
            ans += 1
        elif nine > 0:
            nine -= 1
            ans += 1
        else:
            one += 1
    if s[i] == '5':
        if nine > 0:
            nine -= 1
            ans += 1
print(ans)