use std::io::Read;

fn run() {
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut it = s.trim().split_whitespace();
    let _n: usize = it.next().unwrap().parse().unwrap();
    let s = it.next().unwrap();
    let mut c1 = 0;
    let mut c9 = 0;
    let mut ans = 0;
    for c in s.chars() {
        match c {
            '1' => {
                if c9 >= 2 {
                    ans += 1;
                    c9 -= 2;
                } else {
                    c1 += 1;
                }
            },
            '9' => {
                if c1 >= 1 {
                    ans += 1;
                    c1 -= 1;
                } else {
                    c9 += 1;
                }
            },
            _ => ans += 1,
        }
    }
    while c1 >= 2 {
        ans += 1;
        c1 -= 2;
    }
    println!("{}", ans);
}

fn main() {
    run();
}