#include <cstdio>#include <algorithm>#include <cstring>#define esp 1e-8using namespace std;struct point { double x, y;} all[2008];int n, mark[2008];double aabs(double a) { if (a < 0) return -a; return a;}bool cmp(point p1, point p2) { return (p1.y < p2.y && aabs(p1.y - p2.y) > esp) || (aabs(p1.y - p2.y) <= esp && p1.x < p2.x);}bool mult(point sp, point ep, point op) { return (sp.x - op.x)*(ep.y - op.y) >= (ep.x - op.x)*(sp.y - op.y) - esp;}void hull() { sort(all, all + n, cmp); int res[2009]; memset(mark, 0, sizeof (mark)); int i, len, top = 1; if (n <= 2) return; mark[0] = mark[1] = 1; res[0] = 0; res[1] = 1; for (i = 2; i < n; i++) { while (top && mult(all[i], all[res[top]], all[res[top - 1]])) { mark[res[top--]]--; } res[++top] = i; mark[i]++; } len = top; res[++top] = n - 2; mark[res[top]]++; for (i = n - 3; i >= 0; i--) { while (top != len && mult(all[i], all[res[top]], all[res[top - 1]])) { mark[res[top--]]--; } res[++top] = i; mark[i]++; } int now = 0; for (i = 0; i < n; i++) if (mark[i] <= 0) all[now++] = all[i]; n = now;}int main(int argc, char** argv) { while (scanf("%d", &n) == 1) { for (int i = 0; i < n; i++) { scanf("%lf %lf", &all[i].x, &all[i].y); } int ans = 0; while (n > 2) { hull(); ans++; } printf("%dn", ans); } return 0;}
