#include <stdio.h>
#include <conio.h>
#include <math.h>

#define sqr(val) ((val)*(val))

// #define arrmax 100
#define armax 8

double angle(int x1, int y1, int x2, int y2, int x3, int y3) {
  double l1, l2, l3, cosx;
  l1 = sqrt(sqr(x2-x1)+sqr(y2-y1));
  l2 = sqrt(sqr(x3-x2)+sqr(y3-y2));
  l3 = sqrt(sqr(x3-x1)+sqr(y3-y1));
  cosx = (l1*l1+l2*l2-l3*l3) / (2*l1*l2);
  return acos(cosx);
}

int main() {
    int x[armax] = {3, 6, 6, 5, 7, 7, 4, 9},
        y[armax] = {2, 1, 3, 4, 4, 6, 7, 7}, x1[armax], y1[armax];
    int i, j, n;
    double max_angle;

    clrscr();
    n = 8;
    // puts("Kolichestvo tochek:\n");
    // scanf("%d", &n);
    j = 1;
    max_angle = 0;
    // for(i = 0; i < n; i++) {
    //   printf("x[%d]\n", i); scanf("%d", &x[i]);
    //   printf("y[%d]\n", i); scanf("%d", &y[i]);
    // }

    y1[0] = y[0];
    x1[0] = x[0];
    for(i = 0; i < n; i++) {
        if(y[i] < y1[0]) {
            y1[0] = y[i]; x1[0] = x[i];
        }
        else
            if(y[i] == y1[0] && x[i] > x1[0]) {
                y1[0] = y[i]; x1[0] = x[i];
            }
    }

    for(i = 0; i < n; i++) {
        if(x1[0] != x[i] && y1[0] != y[i])
            if(angle((x1[0]-3),y1[0],x1[0],y1[0],x[i],y[i]) > max_angle) {
              max_angle = angle((x1[0]-3),y1[0],x1[0],y1[0],x[i],y[i]);
              x1[1] = x[i]; y1[1] = y[i];
            }
    }
    do {
        j += 1;
        max_angle = 0;
        for(i = 0; i < n; i++) {
            if(
              (x1[j-2] == x[i] && y1[j-2] == y[i])
              ||
              (x1[j-1] == x[i] && y1[j-1] == y[i])
            ) continue;
            else {
                if(angle(x1[j-2],y1[j-2],x1[j-1],y1[j-1],x[i],y[i]) > max_angle) {
                    max_angle = angle(x1[j-2],y1[j-2],x1[j-1],y1[j-1],x[i],y[i]);
                    x1[j] = x[i];
                    y1[j] = y[i];
                }
            }
        }
    } while(!(x1[j] == x1[0] && y1[j] == y1[0]));
    puts("Obolochka idet cherez tochki:\n");
    for(i = 0; i < j; i++) {
        printf("x[%d]=%d   y[%d]=%d\n", i, x1[i], i, y1[i]);
    }
    getch();
    return 0;
}