double cross(Point a,Point b){    return a.x*b.y-a.y*b.x;}double mul(Point p0,Point p1,Point p2){    return cross(p1-p0,p2-p0);}double dis(Point a){    return sqrt(a.x*a.x+a.y*a.y);}bool cmp(Point a,Point b){    if(dcmp(mul(p[0],a,b))==0)        return dis(a-p[0])<dis(b-p[0]);    else        return dcmp(mul(p[0],a,b))>0;}int Graham(int n){    int i,k = 0,top;    Point tmp;    for(i = 0 ; i < n; i++)    {        if(p[i].y<p[k].y||(p[i].y==p[k].y&&p[i].x<p[k].x))            k = i;    }    if(k!=0)    {        tmp = p[0];        p[0] = p[k];        p[k] = tmp;    }    sort(p+1,p+n,cmp);    ch[0] = p[0];    ch[1] = p[1];    top = 1;    for(i = 2; i < n ; i++)    {        while(top>0&&dcmp(mul(ch[top-1],ch[top],p[i]))<0)            top--;        top++;        ch[top] = p[i];    }    return top;}