#include #include #include #include #include #include #include #include #include #include #include #define rep(i,n) for(int i = 0; i < n; ++i) #define rep1(i,n) for(int i = 1; i <= n; ++i) using namespace std; templatebool chmax(T &a, const T &b) { if(a < b){ a = b; return 1; } return 0; } templatebool chmin(T &a, const T &b) { if(a > b){ a = b; return 1; } return 0; } template inline int sz(T &a) { return a.size(); } using ll = long long; using ld = long double; using pi = pair; using pl = pair; using vi = vector; using vvi = vector; using vl = vector; using vvl = vector; const int inf = numeric_limits::max(); const ll infll = numeric_limits::max(); int main() { int n; cin >> n; vl a(n),b(n); rep(i,n) cin >> a[i] >> b[i]; int res = 0; while(1) { int m = sz(a); vi c(m); rep(i,m) { ll mn = infll; rep(j,m) { if(i == j) continue; ll d = (a[i] - a[j])*(a[i] - a[j]) + (b[i] - b[j])*(b[i] - b[j]); if(chmin(mn, d) ) { c[i] = j; } } } vl x,y; x.push_back(a[0]); y.push_back(a[0]); rep1(i,m-1) { if(c[i] == 0) res++; else if(i == c[c[i]]) { continue; } else { x.push_back(a[i]); y.push_back(b[i]); } } if(sz(x) == 1) break; a = x; b = y; } cout << res << "\n"; return 0; }