/**求出凸包枚举每个点的矩距离即可  因为凸包上的点可定不多。。学习： 刚开始WA 了一次，，因为用int 存的， 一看discuss 里提供的数据，想起来，，应该是越界了。。后来用longlong 就过了。。**/#include 
     
      #include 
      
       #include 
       
        using namespace std;struct point {    long long  x,y;    //point (){}    point (double x=0,double y=0):x(x),y(y){}};point p[50050],ch[50050];typedef point Vector;Vector operator -(point a,point b){    return Vector (a.x-b.x,a.y-b.y);}long long  cross(Vector a,Vector b){    return a.x*b.y-a.y*b.x;}bool cmp(point a,point b){    if(a.x==b.x)        return a.y
        
         1&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0)            m--;        ch[m++] = p[i];    }    int k = m;    for(int i=n-2;i>=0;i--){        while(m>k&&cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0)            m--;        ch[m++] = p[i];    }    if(n>1) m--;    return m;}int main(){    int n;    cin>>n;    for(int i=0;i
         
          >p[i].x>>p[i].y;    }    int m = convexHull(p,n,ch);    long long  max_len = 0;    for(int i=0;i
          
           max_len) max_len = length(ch[j]-ch[i]); } } cout<
           
            <