#ifdef LOCAL #define _GLIBCXX_DEBUG #endif #include using namespace std; #define rep(i,s,t) for(ll i = (ll)(s); i < (ll)(t); i++) #define rrep(i,s,t) for(ll i = (ll)(s-1);(ll)(t) <= i; i--) #define all(x) (x).begin(), (x).end() typedef long long ll; typedef long double ld; typedef pair Pll; typedef vector vl; typedef vector vvl; typedef vector vvvl; constexpr ll INF = numeric_limits::max()/4; constexpr ll n_max = 2e5+10; #define int ll const long double pi = 3.14159265358979323846; template string to_string(pair p); string to_string(const string &s) {return '"' + s + '"';} string to_string(const char *c) {return to_string((string) c);} string to_string(bool b) {return (b ? "true" : "false");} template string to_string(bitset v){ string res = ""; for(size_t i = 0; i < N; i++) res += static_cast('0' + v[i]); return res; } template string to_string(A v) { bool first = true; string res = "{"; for(const auto &x : v) { if(!first) res += ", "; first = false; res += to_string(x); } res += "}"; return res; } template string to_string(pair p){return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";} void debug_out() {cerr << endl;} template void debug_out(Head H, Tail... T) { cerr << " " << to_string(H); debug_out(T...); } #ifdef LOCAL #define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__) #else #define debug(...) 42 #endif template bool chmax(T &a, T b){if(a < b){a = b; return true;} return false;} template bool chmin(T &a, T b){if(a > b){a = b; return true;} return false;} signed main(){ cin.tie(nullptr); ios::sync_with_stdio(false); ll n; cin >> n; vector p(n); rep(i,0,n){ cin >> p[i].first >> p[i].second; } vector> v; rep(i,0,n)rep(j,i+1,n){ double dist = hypot(p[i].first - p[j].first, p[i].second - p[j].second); v.emplace_back(make_tuple(dist, i, j)); } sort(all(v)); vector used(n); ll ans = 0; ll m = v.size(); rep(i,0,m){ auto [d, f, t] = v[i]; if(f == 0){ if(!used[t]){ ans++; used[t] = 1; } } else{ if (used[f] || used[t]) continue; used[f] = 1; used[t] = 1; } } cout << ans << "\n"; }