use std::{collections::BinaryHeap, cmp::Reverse};


fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let ballons = (0..n).map(|_| {
            let mut temp = String::new();
            std::io::stdin().read_line(&mut temp).ok();
            let temp: Vec<isize> = temp.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
            (temp[0], temp[1])
        })
        .collect::<Vec<_>>();

    let mut pque = BinaryHeap::new();
    for i in 0..n {
        let (lx, ly) = ballons[i];
        for j in i+1..n {
            let (rx, ry) = ballons[j];
            let dist = ((lx-rx)*(lx-rx) + (ly-ry)*(ly-ry));
            pque.push((Reverse(dist), i, j));
        }
    }
    let mut bombed = vec![false; n];
    let mut result = 0usize;
    while let Some((_, i, j)) = pque.pop() {
        if bombed[i] || bombed[j] { continue; }
        if i == 0 {
            bombed[j] = true;
            result += 1;
        } else {
            bombed[i] = true;
            bombed[j] = true;
        }
    }
    println!("{}", result);
}