#include <stdlib.h>

struct point { int x, y; char c; };
struct line { struct point p1, p2; };

float theta(struct point p1, struct point p2)
{
    int dx, dy, ax, ay;
    float t;
    dx = p2.x - p1.x; ax = abs(dx);
    dy = p2.y - p1.y; ay = abs(dy);
    t = (ax+ay == 0) ? 0 : (float) dy/(ax+ay);
    if (dx < 0) t = 2-t; else if (dy < 0) t = 4+t;
    return t*90.0;
}

int wrap(struct point p[], int N)
{
    int i, min, M;
    float th, v;
    struct point t;
    for (min = 0, i = 1; i < N; i++)
        if (p[i].y < p[min].y) min = i;
    p[N] = p[min]; th = 0.0;
    for (M = 0; M < N; M++) 
    {
        t = p[M]; p[M] = p[min]; p[min] = t;
        min = N; v = th; th = 360.0;
        for (i = M+1; i <= N; i++)
            if (theta(p[M], p[i]) > v)
                if (theta(p[M], p[i]) < th)
                {
                    min = i; th = theta(p[M], p[min]);
                }
        if (min == N) return M;
    }
    return N;
}