import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop, core.stdc.stdlib, std.datetime;


void main() {
    auto N = readln.chomp.to!int;
    auto A = iota(N).map!(_ => readln.split.map!(to!long).array).array;

    long dist(int i, int j) {
        return (A[i][0] - A[j][0]) ^^ 2 + (A[i][1] - A[j][1]) ^^ 2;
    }

    auto pq = new BinaryHeap!(Array!(Tuple!(int, int, long)), "a[2] > b[2]");
    foreach (i; 0..N) foreach (j; i+1..N) pq.insert(tuple(i, j, dist(i, j)));

    auto used = new bool[](N);
    int ans = 0;

    while (!pq.empty) {
        auto i = pq.front[0];
        auto j = pq.front[1];
        pq.removeFront;
        if (used[i] || used[j]) {
            continue;
        } if (i == 0) {
            ans += 1;
            used[j] = true;
        } else {
            used[i] = used[j] = true;
        }
    }

    ans.writeln;
}