Buggy python submission (verdict: Time Limit Exceeded):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    uf.union(a , b)
    
print(len(uf.all_group_members())-1)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    uf.union(a , b)
    
print(uf.group_count()-1)

Buggy python submission (verdict: Runtime Error):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(int,input().split())
    uf.union(a , b)
    
print(len(uf.all_group_members())-1)


Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    uf.union(a , b)
    
print(uf.group_count()-1)

Buggy python submission (verdict: Time Limit Exceeded):
def find(n):
    if root[n] < 0:
        return n
    else:
        root[n] = find(root[n])
        return root[n]

def unite(x,y):
    x = find(x)
    y = find(y)
    if x == y:
        return
    if root[x] > root[y]:
        x, y = y, x

    root[x] += root[y]
    root[y] = x

def size(x):
    return -root[find(x)]

def same(x,y):
    return find(x) == find(y)

def member(x):
    rt = find(x)
    return [i for i in range(n) if find(i) == rt]

def roots():
    return [i for i, x in enumerate(root) if x < 0]

def member_count(x):
    return len(roots())

def all_group_members():
    return {r: member(r) for r in roots()}

n , m = map(int,input().split())
root = [-1 for i in range(n)]

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    unite(a,b)

print(len(all_group_members())-1)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    uf.union(a , b)
    
print(uf.group_count()-1)

Buggy python submission (verdict: Time Limit Exceeded):
def find(n):
    if root[n] < 0:
        return n
    else:
        root[n] = find(root[n])
        return root[n]

def unite(x,y):
    x = find(x)
    y = find(y)
    if x == y:
        return
    if root[x] > root[y]:
        x, y = y, x

    root[x] += root[y]
    root[y] = x

def size(x):
    return -root[find(x)]

def same(x,y):
    return find(x) == find(y)

def member(x):
    rt = find(x)
    return [i for i in range(n) if find(i) == rt]

def roots():
    return [i for i, x in enumerate(root) if x < 0]

def member_count(x):
    return len(roots())

def all_group_members():
    return {r: member(r) for r in roots()}

n , m = map(int,input().split())
root = [-1 for i in range(n)]

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    unite(a,b)

print(len(all_group_members())-1)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    uf.union(a , b)
    
print(uf.group_count()-1)

Buggy python submission (verdict: Runtime Error):
def find(n):
    if root[n] < 0:
        return n
    else:
        root[n] = find(root[n])
        return root[n]

def unite(x,y):
    x = find(x)
    y = find(y)
    if x == y:
        return
    if root[x] > root[y]:
        x, y = y, x

    root[x] += root[y]
    root[y] = x

def size(x):
    return -root[find(x)]

def same(x,y):
    return find(x) == find(y)

def member(x):
    rt = find(x)
    return [i for i in range(n) if find(i) == rt]

def roots():
    return [i for i, x in enumerate(root) if x < 0]

def member_count(x):
    return len(roots())

def all_group_members():
    return {r: member(r) for r in roots()}

n , m = map(int,input().split())
root = [-1 for i in range(n)]

for _ in range(m):
    a , b = map(int,input().split())
    unite(a,b)

print(len(all_group_members())-1)

Fixed submission:
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

n, m = map(int,input().split())
uf = UnionFind(n)

for _ in range(m):
    a , b = map(lambda x:int(x)-1,input().split())
    uf.union(a , b)
    
print(uf.group_count()-1)