#![allow(unused_imports)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;
use std::ops::Bound::*;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let n = read::<usize>();
    let mut poses = vec![];
    for i in 0..n {
        let v = read_vec::<i64>();
        let (x, y) = (v[0], v[1]);
        poses.push((x, y));
    }

    let mut pairs = vec![];
    for i in 0..n {
        let (xi, yi) = poses[i];
        for j in i + 1..n {
            let (xj, yj) = poses[j];
            let dist = (xi - xj) * (xi - xj) + (yi - yj) * (yi - yj);
            pairs.push((dist, i, j));
        }
    }
    pairs.sort();
    // debug!(pairs);

    let mut used = vec![false; n];
    let mut ans = 0;
    for (_, i, j) in pairs {
        if used[i] || used[j] {
            continue;
        }
        if i != 0 {
            used[i] = true;
            used[j] = true;
        } else {
            used[j] = true;
            ans += 1;
        }
    }
    println!("{}", ans);
}

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> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}