Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque  # 双方向キュー
from collections import defaultdict  # 初期化済み辞書
from heapq import heapify, heappush, heappop, heappushpop  # プライオリティキュー
from bisect import bisect_left, bisect_right  # 二分探索
#import numpy as np  # 1.8.2
#import scipy  # 0.13.3
sys.setrecursionlimit(int(1e+7))  # スタック上限

s2nn = lambda s: [int(c) for c in s.split(' ')]
ss2nn = lambda ss: [int(s) for s in ss]
ss2nnn = lambda ss: [s2nn(s) for s in ss]
i2s = lambda: sys.stdin.readline().rstrip()
i2n = lambda: int(i2s())
i2nn = lambda: s2nn(i2s())
ii2ss = lambda n: [sys.stdin.readline().rstrip() for _ in range(n)]
ii2nn = lambda n: ss2nn(ii2ss(n))
ii2nnn = lambda n: ss2nnn(ii2ss(n))

def main():
    N = i2n()
    XY = ii2nnn(N)
    M = int(1e+5) + 5

    # 二部グラフ
    to = [[] for _ in range(M*2)]
    cnt = [0] * (M*2)
    visited = [False] * (M*2)

    # 二部グラフを構築
    for x, y in XY:
        y += M
        to[x].append(y)
        to[y].append(x)

    cnt = [0, 0]
    def dfs(i):
        visited[i] = True
        cnt[i // M] += 1
        for j in to[i]:
            if visited[j]:
                continue
            dfs(j)

    # 二部グラフを走査
    ans = 0
    for i in range(M*2):
        if visited[i]:
            continue
        cnt[0] = 0
        cnt[1] = 0
        dfs(i)
        ans += cnt[0] * cnt[1]
    
    ans -= N  # 既にある点は操作数に含まれない
    print(ans)

main()


Fixed submission:
import sys
from collections import deque  # 双方向キュー
from collections import defaultdict  # 初期化済み辞書
from heapq import heapify, heappush, heappop, heappushpop  # プライオリティキュー
from bisect import bisect_left, bisect_right  # 二分探索
#import numpy as np  # 1.8.2
#import scipy  # 0.13.3
sys.setrecursionlimit(int(1e+7))  # スタック上限

s2nn = lambda s: [int(c) for c in s.split(' ')]
ss2nn = lambda ss: [int(s) for s in ss]
ss2nnn = lambda ss: [s2nn(s) for s in ss]
i2s = lambda: sys.stdin.readline().rstrip()
i2n = lambda: int(i2s())
i2nn = lambda: s2nn(i2s())
ii2ss = lambda n: [sys.stdin.readline().rstrip() for _ in range(n)]
ii2nn = lambda n: ss2nn(ii2ss(n))
ii2nnn = lambda n: ss2nnn(ii2ss(n))

def main():
    N = i2n()
    XY = ii2nnn(N)
    M = int(1e+5) + 5

    # 二部グラフ
    to = [[] for _ in range(M*2)]
    cnt = [0] * (M*2)
    visited = [False] * (M*2)

    # 二部グラフを構築
    for x, y in XY:
        y += M
        to[x].append(y)
        to[y].append(x)

    cnt = [0, 0]
    def bfs(n):
        q = deque()
        q.append(n)
        while q:
            i = q.popleft()
            if visited[i]:
                continue
            visited[i] = True
            cnt[i // M] += 1
            for j in to[i]:
                q.append(j)

    # 二部グラフを走査
    ans = 0
    for i in range(M*2):
        if visited[i]:
            continue
        cnt[0] = 0
        cnt[1] = 0
        bfs(i)
        ans += cnt[0] * cnt[1]
    
    ans -= N  # 既にある点は操作数に含まれない
    print(ans)

main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from collections import deque  # 双方向キュー
from collections import defaultdict  # 初期化済み辞書
from heapq import heapify, heappush, heappop, heappushpop  # プライオリティキュー
from bisect import bisect_left, bisect_right  # 二分探索
#import numpy as np  # 1.8.2
#import scipy  # 0.13.3
sys.setrecursionlimit(int(1e+7))  # スタック上限

s2nn = lambda s: [int(c) for c in s.split(' ')]
ss2nn = lambda ss: [int(s) for s in ss]
ss2nnn = lambda ss: [s2nn(s) for s in ss]
i2s = lambda: sys.stdin.readline().rstrip()
i2n = lambda: int(i2s())
i2nn = lambda: s2nn(i2s())
ii2ss = lambda n: [sys.stdin.readline().rstrip() for _ in range(n)]
ii2nn = lambda n: ss2nn(ii2ss(n))
ii2nnn = lambda n: ss2nnn(ii2ss(n))

def main():
    N = i2n()
    XY = ii2nnn(N)
    M = int(1e+5) + 5

    # 二部グラフ
    to = [[] for _ in range(M*2)]
    cnt = [0] * (M*2)
    visited = [False] * (M*2)

    # 二部グラフを構築
    for x, y in XY:
        y += M
        to[x].append(y)
        to[y].append(x)

    cnt = [0, 0]
    def dfs(i):
        if visited[i]:
            return
        visited[i] = True
        cnt[i // M] += 1
        for j in to[i]:
            dfs(j)

    # 二部グラフを走査
    ans = 0
    for i in range(M*2):
        if visited[i]:
            continue
        cnt[0] = 0
        cnt[1] = 0
        dfs(i)
        ans += cnt[0] * cnt[1]
    
    ans -= N  # 既にある点は操作数に含まれない
    print(ans)

main()


Fixed submission:
import sys
from collections import deque  # 双方向キュー
from collections import defaultdict  # 初期化済み辞書
from heapq import heapify, heappush, heappop, heappushpop  # プライオリティキュー
from bisect import bisect_left, bisect_right  # 二分探索
#import numpy as np  # 1.8.2
#import scipy  # 0.13.3
sys.setrecursionlimit(int(1e+7))  # スタック上限

s2nn = lambda s: [int(c) for c in s.split(' ')]
ss2nn = lambda ss: [int(s) for s in ss]
ss2nnn = lambda ss: [s2nn(s) for s in ss]
i2s = lambda: sys.stdin.readline().rstrip()
i2n = lambda: int(i2s())
i2nn = lambda: s2nn(i2s())
ii2ss = lambda n: [sys.stdin.readline().rstrip() for _ in range(n)]
ii2nn = lambda n: ss2nn(ii2ss(n))
ii2nnn = lambda n: ss2nnn(ii2ss(n))

def main():
    N = i2n()
    XY = ii2nnn(N)
    M = int(1e+5) + 5

    # 二部グラフ
    to = [[] for _ in range(M*2)]
    cnt = [0] * (M*2)
    visited = [False] * (M*2)

    # 二部グラフを構築
    for x, y in XY:
        y += M
        to[x].append(y)
        to[y].append(x)

    cnt = [0, 0]
    def bfs(n):
        q = deque()
        q.append(n)
        while q:
            i = q.popleft()
            if visited[i]:
                continue
            visited[i] = True
            cnt[i // M] += 1
            for j in to[i]:
                q.append(j)

    # 二部グラフを走査
    ans = 0
    for i in range(M*2):
        if visited[i]:
            continue
        cnt[0] = 0
        cnt[1] = 0
        bfs(i)
        ans += cnt[0] * cnt[1]
    
    ans -= N  # 既にある点は操作数に含まれない
    print(ans)

main()

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque  # 双方向キュー
from collections import defaultdict  # 初期化済み辞書
from heapq import heapify, heappush, heappop, heappushpop  # プライオリティキュー
from bisect import bisect_left, bisect_right  # 二分探索
#import numpy as np  # 1.8.2
#import scipy  # 0.13.3
#sys.setrecursionlimit(int(1e+7))  # スタック上限

s2nn = lambda s: [int(c) for c in s.split(' ')]
ss2nn = lambda ss: [int(s) for s in ss]
ss2nnn = lambda ss: [s2nn(s) for s in ss]
i2s = lambda: sys.stdin.readline().rstrip()
i2n = lambda: int(i2s())
i2nn = lambda: s2nn(i2s())
ii2ss = lambda n: [sys.stdin.readline().rstrip() for _ in range(n)]
ii2nn = lambda n: ss2nn(ii2ss(n))
ii2nnn = lambda n: ss2nnn(ii2ss(n))

def main():
    N = i2n()
    XY = ii2nnn(N)
    M = int(1e+5) + 5

    # 二部グラフ
    to = [[] for _ in range(M*2)]
    cnt = [0] * (M*2)
    visited = [False] * (M*2)

    # 二部グラフを構築
    for x, y in XY:
        y += M
        to[x].append(y)
        to[y].append(x)

    cnt = [0, 0]
    def dfs(i):
        if visited[i]:
            return
        visited[i] = True
        cnt[i // M] += 1
        for j in to[i]:
            dfs(j)

    # 二部グラフを走査
    ans = 0
    for i in range(M*2):
        if visited[i]:
            continue
        cnt[0] = 0
        cnt[1] = 0
        dfs(i)
        ans += cnt[0] * cnt[1]
    
    ans -= N  # 既にある点は操作数に含まれない
    print(ans)

main()


Fixed submission:
import sys
from collections import deque  # 双方向キュー
from collections import defaultdict  # 初期化済み辞書
from heapq import heapify, heappush, heappop, heappushpop  # プライオリティキュー
from bisect import bisect_left, bisect_right  # 二分探索
#import numpy as np  # 1.8.2
#import scipy  # 0.13.3
sys.setrecursionlimit(int(1e+7))  # スタック上限

s2nn = lambda s: [int(c) for c in s.split(' ')]
ss2nn = lambda ss: [int(s) for s in ss]
ss2nnn = lambda ss: [s2nn(s) for s in ss]
i2s = lambda: sys.stdin.readline().rstrip()
i2n = lambda: int(i2s())
i2nn = lambda: s2nn(i2s())
ii2ss = lambda n: [sys.stdin.readline().rstrip() for _ in range(n)]
ii2nn = lambda n: ss2nn(ii2ss(n))
ii2nnn = lambda n: ss2nnn(ii2ss(n))

def main():
    N = i2n()
    XY = ii2nnn(N)
    M = int(1e+5) + 5

    # 二部グラフ
    to = [[] for _ in range(M*2)]
    cnt = [0] * (M*2)
    visited = [False] * (M*2)

    # 二部グラフを構築
    for x, y in XY:
        y += M
        to[x].append(y)
        to[y].append(x)

    cnt = [0, 0]
    def bfs(n):
        q = deque()
        q.append(n)
        while q:
            i = q.popleft()
            if visited[i]:
                continue
            visited[i] = True
            cnt[i // M] += 1
            for j in to[i]:
                q.append(j)

    # 二部グラフを走査
    ans = 0
    for i in range(M*2):
        if visited[i]:
            continue
        cnt[0] = 0
        cnt[1] = 0
        bfs(i)
        ans += cnt[0] * cnt[1]
    
    ans -= N  # 既にある点は操作数に含まれない
    print(ans)

main()