226D.cpp

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using str = string;
using pint = pair<int, int>;
using pll = pair<ll, ll>;
template<class T>using vc = vector<T>;
template<class T>using vvc = vc<vc<T>>;
using vint = vc<int>;
using vll = vc<ll>;
using vstr = vc<str>;
using vpint = vc<pint>;
using vpll = vc<pll>;
using vbool = vc<bool>;
using vvint = vvc<int>;
using vvll = vvc<ll>;

#define overload4(_1, _2, _3, _4, name, ...) name
#define rep1(n)          for(ll i = 0; i < (n); ++i)
#define rep2(i, n)       for(ll i = 0; i < (n); ++i)
#define rep3(i, a, b)    for(ll i = (a); i < (b); ++i)
#define rep4(i, a, b, c) for(ll i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define each1(a)       for(auto&& i : a)
#define each2(i,a)     for(auto&& i : a)
#define each3(x,y,a)   for(auto&& [x, y] : a)
#define each4(x,y,z,a) for(auto&& [x, y, z] : a)
#define each(...) overload4(__VA_ARGS__, each4, each3, each2, each1)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()

void yesno(bool flag){cout << (flag ? "Yes" : "No") << endl;}

ll gcd(ll a, ll b){
    if(b==0) return a;
    return gcd(b, a%b);
}

int main() {
    ll n; cin >> n;
    vpll xy(n);
    rep(n){
        ll x, y; cin >> x >> y;
        xy[i] = {x, y};
    }
    set<pll> s;
    rep(n){
        rep(j,n){
            if(i==j) continue;
            ll dx = xy[j].first - xy[i].first;
            ll dy = xy[j].second - xy[i].second;
            if(dx == 0){
                dy /= abs(dy);
            }else if(dy == 0){
                dx /= abs(dx);
            }else{
                ll g = gcd(abs(dx), abs(dy));
                dx /= g;
                dy /= g;
            }
            s.insert({dx, dy});
        }
    }
    cout << s.size() << endl;
}