Buggy python submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10**7)
def input(): return sys.stdin.readline().rstrip()

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 unite(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 main():
    n, m = map(int, input().split())

    uf = UnionFind(n)
    for _ in range(m):
        a, b = map(int, input().split())
        uf.unite(a-1, b-1)
    roots = uf.roots()
    cnt = []
    for r in roots:
        cnt.append(uf.size(r))
    print(max(cnt))

if __name__ == '__main__':
    main()


Fixed submission:
import sys
sys.setrecursionlimit(10**7)
def input(): return sys.stdin.readline().rstrip()

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 unite(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 main():
    n, m = map(int, input().split())

    uf = UnionFind(n)
    for _ in range(m):
        a, b = map(int, input().split())
        uf.unite(a-1, b-1)
    roots = uf.roots()
    cnt = []
    for r in roots:
        cnt.append(uf.size(r))
    print(max(cnt))

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10**7)
def input(): return sys.stdin.readline().rstrip()

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 unite(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 main():
    n, m = map(int, input().split())

    uf = UnionFind(n)
    for _ in range(m):
        a, b = map(int, input().split())
        uf.unite(a-1, b-1)
    roots = uf.roots()
    cnt = []
    for r in roots:
        cnt.append(uf.size(r))
    print(max(cnt))

if __name__ == '__main__':
    main()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)
def input(): return sys.stdin.readline().rstrip()

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 unite(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 main():
    n, m = map(int, input().split())

    uf = UnionFind(n)
    for _ in range(m):
        a, b = map(int, input().split())
        uf.unite(a-1, b-1)
    roots = uf.roots()
    cnt = []
    for r in roots:
        cnt.append(uf.size(r))
    print(max(cnt))

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
sys.setrecursionlimit(10**7)
def input(): return sys.stdin.readline().rstrip()


def main():
    n, m = map(int, input().split())
    l = {}
    for _ in range(m-1):
        a, b = sorted(map(int, input().split()))
        if a not in l:
            l[a] = {b}
        else:
            l[a].add(b)
    i = max(l, key=lambda k: len(l[k]))
    print(len(l[i]) + 1)


if __name__ == '__main__':
    main()

Fixed submission:
import sys
sys.setrecursionlimit(10**7)
def input(): return sys.stdin.readline().rstrip()

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 unite(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 main():
    n, m = map(int, input().split())

    uf = UnionFind(n)
    for _ in range(m):
        a, b = map(int, input().split())
        uf.unite(a-1, b-1)
    roots = uf.roots()
    cnt = []
    for r in roots:
        cnt.append(uf.size(r))
    print(max(cnt))

if __name__ == '__main__':
    main()