use std::io::{self, BufRead};

fn main() {
    let input = io::stdin()
        .lock()
        .lines()
        .flat_map(|l| {
            l.unwrap()
                .split_whitespace()
                .map(|n| n.parse::<usize>().unwrap())
                .collect::<Vec<_>>()
        })
        .collect::<Vec<_>>();

    let counts = (1..=10)
        .map(|i| input[1..].iter().filter(|&&n| n == i).count())
        .collect::<Vec<_>>();

    let n_pairs = counts.iter().map(|i| i / 2).sum::<usize>();
    let n_fours = counts.iter().map(|i| i % 2).sum::<usize>() / 4;

    println!("{}", n_pairs + n_fours);
}