Buggy python submission (verdict: Runtime Error):
V=10**5
class UnionFind:
    def __init__(self,n):
        self.parent=[i for i in range(n)]
        self.rank=[0 for _ in range(n)]
        # use for n=2*V
        self.xSize=[1 if i<V else 0 for i in range(n)]
        self.ySize=[0 if i<V else 1 for i in range(n)]

    def find(self,x):
        if self.parent[x]==x:
            return x
        else:
            parentx=self.find(self.parent[x])
            self.parent[x]=parentx
            return parentx

    def union(self,x,y):
        rootx=self.find(x)
        rooty=self.find(y)
        if self.rank[rootx]>self.rank[rooty]:
            self.parent[rooty]=rootx
            self.xSize[rootx]+=self.xSize[rooty]
            self.ySize[rootx]+=self.ySize[rooty]
        else:
            self.parent[rootx]=rooty
            self.xSize[rooty]+=self.xSize[rootx]
            self.ySize[rooty]+=self.ySize[rootx]
            if self.rank[rootx]==self.rank[rooty]:
                self.rank[rooty]+=1

n=int(input())
xy=[list(map(int,input().split())) for _ in range(n)]
uf=UnionFind(V*2)
for xi,yi in xy:
    uf.union(xi,yi+V)

for i in range(V*2):
    uf.find(i)

ans=0
used=set()
for i in range(V*2):
    rooti=uf.find(i)
    if rooti not in used:
        used.add(rooti)
        ans+= uf.xSize[rooti]*uf.ySize[rooti]
print(ans-n)


Fixed submission:
V=10**5+5
class UnionFind:
    def __init__(self,n):
        self.parent=[i for i in range(n)]
        self.rank=[0 for _ in range(n)]
        # use for n=2*V
        self.xSize=[1 if i<V else 0 for i in range(n)]
        self.ySize=[0 if i<V else 1 for i in range(n)]

    def find(self,x):
        if self.parent[x]==x:
            return x
        else:
            parentx=self.find(self.parent[x])
            self.parent[x]=parentx
            return parentx

    def union(self,x,y):
        rootx=self.find(x)
        rooty=self.find(y)
        if rootx==rooty:
            return
        if self.rank[rootx]>self.rank[rooty]:
            self.parent[rooty]=rootx
            self.xSize[rootx]+=self.xSize[rooty]
            self.ySize[rootx]+=self.ySize[rooty]
        else:
            self.parent[rootx]=rooty
            self.xSize[rooty]+=self.xSize[rootx]
            self.ySize[rooty]+=self.ySize[rootx]
            if self.rank[rootx]==self.rank[rooty]:
                self.rank[rooty]+=1

n=int(input())
xy=[tuple(map(int,input().split())) for _ in range(n)]
uf=UnionFind(V*2)
for xi,yi in xy:
    uf.union(xi,yi+V)

# for i in range(V*2):
#     uf.find(i)

ans=0
used=set()
for i in range(V*2):
    rooti=uf.find(i)
    if rooti not in used:
        used.add(rooti)
        ans+= uf.xSize[rooti]*uf.ySize[rooti]
print(ans-n)

Buggy python submission (verdict: Runtime Error):
V=10**5
class UnionFind:
    def __init__(self,n):
        self.parent=[i for i in range(n)]
        self.rank=[0 for _ in range(n)]
        # use for n=2*V
        self.xSize=[1 if i<V else 0 for i in range(n)]
        self.ySize=[0 if i<V else 1 for i in range(n)]

    def find(self,x):
        if self.parent[x]==x:
            return x
        else:
            parentx=self.find(self.parent[x])
            self.parent[x]=parentx
            return parentx

    def union(self,x,y):
        rootx=self.find(x)
        rooty=self.find(y)
        if self.rank[rootx]>self.rank[rooty]:
            self.parent[rooty]=rootx
            self.xSize[rootx]+=self.xSize[rooty]
            self.ySize[rootx]+=self.ySize[rooty]
        else:
            self.parent[rootx]=rooty
            self.xSize[rooty]+=self.xSize[rootx]
            self.ySize[rooty]+=self.ySize[rootx]
            if self.rank[rootx]==self.rank[rooty]:
                self.rank[rooty]+=1

n=int(input())
xy=[list(map(int,input().split())) for _ in range(n)]
uf=UnionFind(V*2)
for xi,yi in xy:
    uf.union(xi,yi+V)

ans=0
used=set()
for i in range(V*2):
    rooti=uf.find(i)
    if rooti not in used:
        used.add(rooti)
        ans+= uf.xSize[rooti]*uf.ySize[rooti]
print(ans-n)


Fixed submission:
V=10**5+5
class UnionFind:
    def __init__(self,n):
        self.parent=[i for i in range(n)]
        self.rank=[0 for _ in range(n)]
        # use for n=2*V
        self.xSize=[1 if i<V else 0 for i in range(n)]
        self.ySize=[0 if i<V else 1 for i in range(n)]

    def find(self,x):
        if self.parent[x]==x:
            return x
        else:
            parentx=self.find(self.parent[x])
            self.parent[x]=parentx
            return parentx

    def union(self,x,y):
        rootx=self.find(x)
        rooty=self.find(y)
        if rootx==rooty:
            return
        if self.rank[rootx]>self.rank[rooty]:
            self.parent[rooty]=rootx
            self.xSize[rootx]+=self.xSize[rooty]
            self.ySize[rootx]+=self.ySize[rooty]
        else:
            self.parent[rootx]=rooty
            self.xSize[rooty]+=self.xSize[rootx]
            self.ySize[rooty]+=self.ySize[rootx]
            if self.rank[rootx]==self.rank[rooty]:
                self.rank[rooty]+=1

n=int(input())
xy=[tuple(map(int,input().split())) for _ in range(n)]
uf=UnionFind(V*2)
for xi,yi in xy:
    uf.union(xi,yi+V)

# for i in range(V*2):
#     uf.find(i)

ans=0
used=set()
for i in range(V*2):
    rooti=uf.find(i)
    if rooti not in used:
        used.add(rooti)
        ans+= uf.xSize[rooti]*uf.ySize[rooti]
print(ans-n)