fn main() {
    let n: u32 = read();
    let mat: Vec<Vec<u32>> = read_mat(n);
    let mut count = [0u32; 11];

    for row in mat {
        for e in row {
            count[e as usize] += 1;
        }
    }

    let mut powerup = 0u32;
    let mut rest = 0u32;
    for i in &mut count {
        powerup += *i/2;
        rest += *i%2;
    }

    powerup += rest/4;

    println!("{}", powerup);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().split_whitespace()
        .map(|e| e.parse().ok().unwrap()).collect()
}

fn read_mat<T: std::str::FromStr>(row: u32) -> Vec<Vec<T>> {
    let mut vec = Vec::new();

    for _i in 0..row {
        vec.push(read_vec::<T>());
    }

    vec
}