Buggy python submission (verdict: Runtime Error):
from collections import defaultdict, deque

N, M = map(int, input().split())

D = defaultdict(deque)
R = [0] * (N+1)
for _ in range(M):
  a, b = map(int, input().split())
  if R[a] != 0:
    if R[b] != 0:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa].extend(D[bb])
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].append(b)
  else:
    if R[b] != 0:
      R[a] = R[b]
      D[R[b]].append(a)
    else:
      R[a] = a
      R[b] = a
      D[a].append(a)
      D[a].append(b)

print(max(len(x) for x in D.values()))

Fixed submission:
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()) if D else 1)

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()))

Fixed submission:
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()) if D else 1)

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()))

Fixed submission:
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()) if D else 1)

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()))

Fixed submission:
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()) if D else 1)

Buggy python submission (verdict: Runtime Error):
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(b)

print(max(len(x) for x in D.values()) + 1)

Fixed submission:
from collections import defaultdict

N, M = map(int, input().split())

D = defaultdict(set)
R = {}
for _ in range(M):
  a, b = map(int, input().split())
  if a in R:
    if b in R:
      aa, bb = R[a], R[b] 
      if aa == bb:
        pass
      else:
        if len(D[aa]) < len(D[bb]):
          aa, bb = bb, aa
        for x in D[bb]:
          R[x] = aa
        D[aa] |= D[bb]
        del D[bb]
    else:
      R[b] = R[a]
      D[R[a]].add(b)
  else:
    if b in R:
      R[a] = R[b]
      D[R[b]].add(a)
    else:
      R[a] = a
      R[b] = a
      D[a].add(a)
      D[a].add(b)

print(max(len(x) for x in D.values()) if D else 1)