#include<iostream>
#include<algorithm>
#define out cout
#define in cin
#define f for
using namespace std;
struct why
{
	int x,y;
}a[10000];
bool cmp(why a,why b)
{
	if(!a.x==b.x)return a.x<b.x;
	else return a.y<b.y;
}
int bol[10000],xy;
int main()
{
	int n,max,may;
	in>>n;
	f(int i=0;i<n;i++)
	{
		in>>a[i].x>>a[i].y;
		if(a[i].x>max)max=a[i].x;
		if(a[i].y>may)may=a[i].y;
	}
	sort(a,a+n,cmp);
	int sha=0;
	f(int i=may-1;i>=0;i--)
	{
		if(i==may-1)sha=a[i].x,bol[++xy]=i;
		else if(a[i].x>sha)sha=a[i].x,bol[++xy]=i;
	}
	f(int i=2;i<=xy;i++)
	{
		out<<'('<<a[bol[i]].x<<','<<a[bol[i]].y<<')';
		if(i!=xy)cout<<',';
	}
}

40分，除第一个WA，其余都RE。