#include #define rep(i,n) for(int i = 0; i < (int)(n); i++) #define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--) #define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++) #define rrep2(ri,x,n) for(int ri = (int)(n-1); ri >= (int)(x); ri--) #define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++) #define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++) #define ALL(x) x.begin(), x.end() using ll = long long; using namespace std; int main(){ int n; cin >> n; pair ms; int a, b; cin >> a >> b; ms = {a, b}; vector> ab(n-1); rep(i, n-1){ int a, b; cin >> a >> b; ab.at(i) = {a, b}; } int ans = 0; vector chk(n-1, false); vector dv(n-1); set>> se; rep(i, n-1){ auto [a, b] = ab.at(i); double d = hypot(ms.first - a, ms.second - b); dv.at(i) = d; rep2(j, i+1, n-1){ auto [a2, b2] = ab.at(j); double dis = hypot(a - a2, b - b2); se.insert({dis, {i, j}}); } } for(auto pp : se){ auto [dis, ij] = pp; auto [i, j] = ij; if(chk.at(i) == true || chk.at(j) == true) continue; if(dv.at(i) < dis || dv.at(j) < dis) continue; chk.at(i) = true; chk.at(j) = true; } rep(i, n-1){ if(chk.at(i) == false) ans++; } cout << ans << endl; return 0; }