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 Python (3.4.3) (judge verdict: Wrong Answer)

#!/usr/bin/env python3
import sys
from collections.abc import Iterable
from math import *
from itertools import *
from collections import *
from functools import *
from operator import *
try:
    from math import gcd
except Exception:
    from fractions import gcd


class DGraph:
    def __init__(self, n, edges):
        self._vertice = [{} for _ in range(n)]
        for e in edges:
            self._vertice[e[0]][e[1]] = e[2] if len(e) == 3 else 1

    def __len__(self):
        return len(self._vertice)

    def edges(self, n=None):
        srcs = range(len(self)) if n is None else [n]
        return sum([[(s, d, c) for d, c in self._vertice[s].items()] for s in srcs], [])

    def transpose(self):
        tedges = [(t, f, c) for f, t, c in self.edges()]
        return DGraph(len(self), tedges)

    def cost(self, src, dst):
        return self._vertice[src].get(dst, float('inf'))

class Graph(DGraph):
    def __init__(self, n, edges):
        nd_edges = edges + [(d, s, c) for s, d, c in edges]
        super().__init__(n, nd_edges)

    def transpose(self):
        return self


def solve(N: int, x: "List[int]", y: "List[int]"):
    xs = {v:i for i, v in enumerate(set(x))}
    ys = {v:i for i, v in enumerate(set(y), len(xs))}
    
    n = len(xs) + len(ys)
    es = [(xs[cx], ys[cy], 1) for cx, cy in zip(x, y)]
    g = Graph(n, es)

    visited = [False] * len(g)
    def dfs(g, src):
        nonlocal visited
        stack = [(src, 0)]
        while stack:
            n, c = stack.pop()
            if visited[n]:
                continue
            visited[n] = True

            for _, d, _ in g.edges(n):
                #yield d
                stack.append((d, c + 1))
            yield n, c

    def _f(i):
        ls = list(i)
        if len(ls) == 0:
            return None

        xc = 0
        yc = 0
        for i, _ in ls:
            if i < len(xs):
                xc += 1
            else:
                yc += 1

        if xc < 2 or yc < 2:
            return None

        return xc * yc

    l = [v for v in [_f(dfs(g, i)) for i in range(n)] if v is not None]
    acc = 0 if len(l) == 0 else sum(l)
    acc -= N

    return max(acc, 0)


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    x = [int()] * (N)  # type: "List[int]" 
    y = [int()] * (N)  # type: "List[int]" 
    for i in range(N):
        x[i] = int(next(tokens))
        y[i] = int(next(tokens))
    result = solve(N, x, y)
    if isinstance(result, Iterable) and not isinstance(result, str):
        result = '\n'.join([str(v) for v in result])
    print(result)

if __name__ == '__main__':
    main()