Problem:
Score : 600 points

Problem Statement

There are N dots in a two-dimensional plane. The coordinates of the i-th dot are (x_i, y_i).

We will repeat the following operation as long as possible:

Choose four integers a, b, c, d (a \neq c, b \neq d) such that there are dots at exactly three of the positions (a, b), (a, d), (c, b) and (c, d), and add a dot at the remaining position.

We can prove that we can only do this operation a finite number of times. Find the maximum number of times we can do the operation.

Constraints

1 \leq N \leq 10^5

1 \leq x_i, y_i \leq 10^5

If i \neq j, x_i \neq x_j or y_i \neq y_j.

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
x_1 y_1
:
x_N y_N

Output

Print the maximum number of times we can do the operation.

Sample Input 1

3
1 1
5 1
5 5

Sample Output 1

1

By choosing a = 1, b = 1, c = 5, d = 5, we can add a dot at (1, 5). We cannot do the operation any more, so the maximum number of operations is 1.

Sample Input 2

2
10 10
20 20

Sample Output 2

0

There are only two dots, so we cannot do the operation at all.

Sample Input 3

9
1 1
2 1
3 1
4 1
5 1
1 2
1 3
1 4
1 5

Sample Output 3

16

We can do the operation for all choices of the form a = 1, b = 1, c = i, d = j (2 \leq i,j \leq 5), and no more. Thus, the maximum number of operations is 16.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Collections;
using System.Collections.Specialized;
using System.Linq;
using System.Text;
using System.IO;
using System.Reflection;
using static System.Math;
using System.Numerics;
static class Program{
	const int mod=(int)1e9+7;
	static void Main(){
		Sc sc=new Sc();
		var n=sc.I;
		var hx=new Dictionary<int,int>();
		var hy=new Dictionary<int,int>();
		int[] x=new int[n];
		int[] y=new int[n];
		bool[] b=new bool[n];
		Uf uf=new Uf(n);
		for(int i = 0;i<n;i++) {
			var e=sc.Ia;
			if(hx.ContainsKey(e[0])){uf.Union(i,hx[e[0]]);}
			else{hx.Add(e[0],i);}
			if(hy.ContainsKey(e[1])){uf.Union(i,hy[e[1]]);}
			else{hy.Add(e[1],i);}
		}
		foreach(var e in hx){x[uf.Root(e.Value)]++;}
		foreach(var e in hy){y[uf.Root(e.Value)]++;}
		long ans=0;
		for(int i = 0;i<n;i++) {
			if(b[uf.Root(i)]){continue;}
			b[uf.Root(i)]=true;
			ans+=(long)x[uf.Root(i)]*y[uf.Root(i)]-uf.Total(i);
		}
		Console.WriteLine("{0}",ans);
	}
}
public class Uf{
	private int[] arr,hi;
	public int all;
	public Uf(int n){
		arr=new int[n];
		hi=new int[n];
		all=n;
		for(int i=0;i<n;i++){arr[i]=-1;}
	}
	public void Union(int a,int b){
		a=Root(a);
		b=Root(b);
		if(a!=b){
			if(hi[a]<hi[b]){
				int v=b;
				b=a;
				a=v;
			}
			arr[a]+=arr[b];
			hi[a]=Math.Max(hi[a],hi[b]+1);
			arr[b]=a;
			all--;
		}
	}
	public bool Same(int a,int b){return Root(a)==Root(b);}
	public int Total(int a){return -arr[Root(a)];}
	public int Root(int a){return arr[a]<0?a:arr[a]=Root(arr[a]);}
}


public class Sc{
	public int I{get{return int.Parse(Console.ReadLine());}}
	public long L{get{return long.Parse(Console.ReadLine());}}
	public double D{get{return double.Parse(Console.ReadLine());}}
	public string S{get{return Console.ReadLine();}}
	public int[] Ia{get{return Array.ConvertAll(Console.ReadLine().Split(),int.Parse);}}
	public long[] La{get{return Array.ConvertAll(Console.ReadLine().Split(),long.Parse);}}
	public double[] Da{get{return Array.ConvertAll(Console.ReadLine().Split(),double.Parse);}}
	public string[] Sa{get{return Console.ReadLine().Split();}}
	public object[] Oa{get{return Console.ReadLine().Split();}}
	public int[] Ia2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),int.Parse);}}
	public int[] Ia3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),int.Parse);}
	public int[] Ia3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),int.Parse);}
	public long[] La2{get{return Array.ConvertAll(("0 "+Console.ReadLine()+" 0").Split(),long.Parse);}}
	public long[] La3(int a){return Array.ConvertAll((a.ToString()+" "+Console.ReadLine()).Split(),long.Parse);}
	public long[] La3(bool a,int b,bool c,int d){return Array.ConvertAll(((a?b.ToString()+" ":"")+Console.ReadLine()+(c?" "+d.ToString():"")).Split(),long.Parse);}
	public T[] Arr<T>(int n,Func<T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f();}return a;}
	public T[] Arr<T>(int n,Func<int,T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i);}return a;}
	public T[] Arr<T>(int n,Func<string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(Console.ReadLine().Split());}return a;}
	public T[] Arr<T>(int n,Func<int,string[],T> f){var a=new T[n];for(int i=0;i<n;i++){a[i]=f(i,Console.ReadLine().Split());}return a;}
}