Buggy python submission (verdict: Time Limit Exceeded):
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))

def do():
    n,m=INTM()
    frd=[[False]*n]
    #print(frd)
    for i in range(m):
        a,b=INTM()
        flg=True
        for k in range(len(frd)):
            if frd[k][a-1] or frd[k][b-1]:
                if not(frd[k][a-1]):
                    frd[k][a-1]=True
                if not(frd[k][b-1]):
                    frd[k][b-1]=True
                flg=False
                break
        if flg:
            temp=[False]*n
            temp[a-1]=True
            temp[b-1]=True
            frd.append(temp)
            
            
                
    #print(frd)
    ans=1
    for i in range(len(frd)):
        ans=max(ans,sum(frd[i]))
    
    print(ans)

                
if __name__=='__main__':
    do()

Fixed submission:
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))
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())


def do():
    n,m=INTM()
    uf=UnionFind(n)
    for i in range(m):
        a,b=INTM()
        uf.union(a-1,b-1)

    ans=0

    for i in range(n):
        ans=max(ans,uf.size(i))
    
    print(ans)
                
if __name__=='__main__':
    do()

Buggy python submission (verdict: Time Limit Exceeded):
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))

def do():
    n,m=INTM()
    frd=[[0]]
    #print(frd)
    for i in range(m):
        a,b=INTM()
        flg=True
        for k in range(len(frd)):
            if ((a in frd[k])or(b in frd[k])):
                if not(a in frd[k]):
                    frd[k].append(a)
                if not(b in frd[k]):
                    frd[k].append(b)
                flg=False
                break
        if flg:
            frd.append([a,b])
            
                
    #print(frd)
    ans=1
    for i in range(len(frd)):
        ans=max(ans,len(frd[i]))
    
    print(ans)

                
if __name__=='__main__':
    do()

Fixed submission:
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))
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())


def do():
    n,m=INTM()
    uf=UnionFind(n)
    for i in range(m):
        a,b=INTM()
        uf.union(a-1,b-1)

    ans=0

    for i in range(n):
        ans=max(ans,uf.size(i))
    
    print(ans)
                
if __name__=='__main__':
    do()

Buggy python submission (verdict: Time Limit Exceeded):
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))

def do():
    n,m=INTM()
    frd=[[] for i in range(n)]
    #print(frd)
    for i in range(m):
        a,b=INTM()
        for k in range(n):
            if ((a in frd[k])or(b in frd[k])):
                if not(a in frd[k]):
                    frd[k].append(a)
                if not(b in frd[k]):
                    frd[k].append(b)
                break
            elif frd[k]==[]:
                frd[k].append(a)
                frd[k].append(b)
                break
            else:
                pass
                
    #print(frd)
    ans=1
    for i in range(n):
        ans=max(ans,len(frd[i]))
    
    print(ans)

                
if __name__=='__main__':
    do()

Fixed submission:
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))
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())


def do():
    n,m=INTM()
    uf=UnionFind(n)
    for i in range(m):
        a,b=INTM()
        uf.union(a-1,b-1)

    ans=0

    for i in range(n):
        ans=max(ans,uf.size(i))
    
    print(ans)
                
if __name__=='__main__':
    do()

Buggy python submission (verdict: Time Limit Exceeded):
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))

def do():
    n,m=INTM()
    frd=[[] for i in range(n)]
    #print(frd)
    for i in range(m):
        a,b=INTM()
        for k in range(n):
            if ((a in frd[k])or(b in frd[k])):
                if not(a in frd[k]):
                    frd[k].append(a)
                if not(b in frd[k]):
                    frd[k].append(b)
                break
            elif frd[k]==[]:
                frd[k].append(a)
                frd[k].append(b)
    
    ans=1
    for i in range(n):
        ans=max(ans,len(frd[i]))
    
    print(ans)

                
if __name__=='__main__':
    do()

Fixed submission:
INT = lambda: int(input())
INTM = lambda: map(int,input().split())
STRM = lambda: map(str,input().split())
STR = lambda: str(input())
LIST = lambda: list(map(int,input().split()))
LISTS = lambda: list(map(str,input().split()))
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())


def do():
    n,m=INTM()
    uf=UnionFind(n)
    for i in range(m):
        a,b=INTM()
        uf.union(a-1,b-1)

    ans=0

    for i in range(n):
        ans=max(ans,uf.size(i))
    
    print(ans)
                
if __name__=='__main__':
    do()