#![allow(dead_code, unused_mut)]
#![allow(non_snake_case)]

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let mut s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

fn main() {
    input!{
        n: usize,
        l: [(i64, i64); n]
    }
    let mut g = Vec::new();
    for i in 0..n-1 {
        for j in i+1..n {
            g.push(((l[i].0 - l[j].0).pow(2) + (l[i].1 - l[j].1).pow(2), i, j));
        }
    }
    g.sort();
    let mut cnt = 0;
    let mut f = vec![true; n];
    for &(_, i, j) in g.iter() {
        if i == 0 && f[j] {
            cnt += 1;
            f[j] = false;
        } else if f[i] && f[j] {
            f[i] = false;
            f[j] = false;
        }
    }
    println!("{}", cnt);
}