Buggy python submission (verdict: Runtime Error):
from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inpl(): return list(map(int, input().split()))
def inpl_str(): return list(input().split())

class UnionFind:
    def __init__(self,N): # 頂点数 N
        self.table = [i for i in range(N)]    #木の親 table[x] == x なら根
        self.rank  = [1 for i in range(N)]    #木の長さ
        self.size  = [1 for i in range(N)]    #集合のサイズ

    def Find(self,x):    #xの根を返す
        if self.table[x] == x:
            return x
        else:
            self.table[x] = self.Find(self.table[x])    #親の更新(根を直接親にして参照距離を短く)
            self.size[x] = self.size[self.table[x]]
            return self.table[x]

    def Unite(self,x,y):    #xとyを繋げる
        x,y = self.Find(x), self.Find(y)
        sx,sy = self.Size(x), self.Size(y)
        if x == y: return
        if self.rank[x] > self.rank[y]:
            self.table[y] = x
            self.size[x] = sx + sy
        else:
            self.table[x] = y
            self.size[y] = sx + sy
            if self.rank[x] == self.rank[y]:
                self.rank[y] += 1

    def Check(self,x,y):
        return self.Find(x) == self.Find(y)

    def Size(self,x):
        return self.size[self.Find(x)]



N = int(input())
UF = UnionFind(N)

xys = [inpl() for _ in range(N)]
xys.sort()
tatedict = defaultdict(list)
xx = set()
for x,y in xys:
    tatedict[x].append(y)
    xx.add(x)

for x in xx:
    s = tatedict[x][0]
    for t in tatedict[x]:
        if not UF.Check(s,t):
            UF.Unite(s,t)

ans = 0
for x in xx:
    s = tatedict[x][0]
    ans += UF.Size(s) - len(tatedict[x])

print(ans)


Fixed submission:
from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inpl(): return list(map(int, input().split()))
def inpl_str(): return list(input().split())

def Find(x):    #xの根を返す
    global table

    if table[x] == x:
        return x
    else:
        table[x] = Find(table[x])    #親の更新(根を直接親にして参照距離を短く)
        size[x] = size[table[x]]
        return table[x]

def Unite(x,y):    #xとyを繋げる
    global size
    global rank
    x = Find(x)
    y = Find(y)
    sx = Size(x)
    sy = Size(y)

    if x == y:
        return

    if rank[x] > rank[y]:
        table[y] = x
        size[x] = sx + sy
    else:
        table[x] = y
        size[y] = sx + sy
        if rank[x] == rank[y]:
            rank[y] += 1

def Check(x,y):
    if Find(x) == Find(y):
        return True
    else:
        return False

def Size(x):
    return size[Find(x)]

table = [i for i in range(10**5+1)]    #木の親 table[x] == x なら根
rank  = [1 for i in range(10**5+1)]    #木の長さ
size  = [1 for i in range(10**5+1)]    #集合のサイズ


N = int(input())
xys = [inpl() for _ in range(N)]
xys.sort()
tatedict = defaultdict(list)
xx = set()
for x,y in xys:
    tatedict[x].append(y)
    xx.add(x)

for x in xx:
    s = tatedict[x][0]
    for t in tatedict[x]:
        if not Check(s,t):
            Unite(s,t)

ans = 0
for x in xx:
    s = tatedict[x][0]
    ans += Size(s) - len(tatedict[x])

print(ans)