Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# FileName: 	D
# CreatedDate:  2020-08-29 21:38:12 +0900
# LastModified: 2020-08-29 21:53:47 +0900
#


import os
import sys
sys.setrecursionlimit(100000)
# import numpy as np
# import pandas as pd
from collections import Counter


def dfs(u, color, path, n, d):
    color[u] = d
    for v in path[u]:
        if color[v] == -1:
            dfs(v, color, path, n, d)



def main():
    n, m = map(int, input().split())
    path = [[] for _ in range(n+1)]
    for _ in range(m):
        a, b = map(int, input().split())
        path[a].append(b)
        path[b].append(a)
    color = [-1]*(n+1)
    d = 0
    for i in range(1, n+1):
        if color[i] == -1:
            dfs(i, color, path, n, d)
            d += 1
    color = color[1:]
    color_cnt = Counter(color).values()
    print(max(color_cnt))



if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# FileName: 	D
# CreatedDate:  2020-08-29 21:38:12 +0900
# LastModified: 2020-08-29 21:54:27 +0900
#


import os
import sys
sys.setrecursionlimit(900000)
# import numpy as np
# import pandas as pd
from collections import Counter


def dfs(u, color, path, n, d):
    color[u] = d
    for v in path[u]:
        if color[v] == -1:
            dfs(v, color, path, n, d)



def main():
    n, m = map(int, input().split())
    path = [[] for _ in range(n+1)]
    for _ in range(m):
        a, b = map(int, input().split())
        path[a].append(b)
        path[b].append(a)
    color = [-1]*(n+1)
    d = 0
    for i in range(1, n+1):
        if color[i] == -1:
            dfs(i, color, path, n, d)
            d += 1
    color = color[1:]
    color_cnt = Counter(color).values()
    print(max(color_cnt))



if __name__ == "__main__":
    main()

Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# FileName: 	D
# CreatedDate:  2020-08-29 21:38:12 +0900
# LastModified: 2020-08-29 21:52:24 +0900
#


import os
import sys
sys.setrecursionlimit(20000)
# import numpy as np
# import pandas as pd
from collections import Counter


def dfs(u, color, path, n, d):
    color[u] = d
    for v in path[u]:
        if color[v] == -1:
            dfs(v, color, path, n, d)



def main():
    n, m = map(int, input().split())
    path = [[] for _ in range(n+1)]
    for _ in range(m):
        a, b = map(int, input().split())
        path[a].append(b)
        path[b].append(a)
    color = [-1]*(n+1)
    d = 0
    for i in range(1, n+1):
        if color[i] == -1:
            dfs(i, color, path, n, d)
            d += 1
    color = color[1:]
    color_cnt = Counter(color).values()
    print(max(color_cnt))



if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# FileName: 	D
# CreatedDate:  2020-08-29 21:38:12 +0900
# LastModified: 2020-08-29 21:54:27 +0900
#


import os
import sys
sys.setrecursionlimit(900000)
# import numpy as np
# import pandas as pd
from collections import Counter


def dfs(u, color, path, n, d):
    color[u] = d
    for v in path[u]:
        if color[v] == -1:
            dfs(v, color, path, n, d)



def main():
    n, m = map(int, input().split())
    path = [[] for _ in range(n+1)]
    for _ in range(m):
        a, b = map(int, input().split())
        path[a].append(b)
        path[b].append(a)
    color = [-1]*(n+1)
    d = 0
    for i in range(1, n+1):
        if color[i] == -1:
            dfs(i, color, path, n, d)
            d += 1
    color = color[1:]
    color_cnt = Counter(color).values()
    print(max(color_cnt))



if __name__ == "__main__":
    main()

Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# FileName: 	D
# CreatedDate:  2020-08-29 21:38:12 +0900
# LastModified: 2020-08-29 21:51:01 +0900
#


import os
import sys
# import numpy as np
# import pandas as pd
from collections import Counter


def dfs(u, color, path, n, d):
    color[u] = d
    for v in path[u]:
        if color[v] == -1:
            dfs(v, color, path, n, d)



def main():
    n, m = map(int, input().split())
    path = [[] for _ in range(n+1)]
    for _ in range(m):
        a, b = map(int, input().split())
        path[a].append(b)
        path[b].append(a)
    color = [-1]*(n+1)
    d = 0
    for i in range(1, n+1):
        if color[i] == -1:
            dfs(i, color, path, n, d)
            d += 1
    color = color[1:]
    color_cnt = Counter(color).values()
    print(max(color_cnt))



if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# FileName: 	D
# CreatedDate:  2020-08-29 21:38:12 +0900
# LastModified: 2020-08-29 21:54:27 +0900
#


import os
import sys
sys.setrecursionlimit(900000)
# import numpy as np
# import pandas as pd
from collections import Counter


def dfs(u, color, path, n, d):
    color[u] = d
    for v in path[u]:
        if color[v] == -1:
            dfs(v, color, path, n, d)



def main():
    n, m = map(int, input().split())
    path = [[] for _ in range(n+1)]
    for _ in range(m):
        a, b = map(int, input().split())
        path[a].append(b)
        path[b].append(a)
    color = [-1]*(n+1)
    d = 0
    for i in range(1, n+1):
        if color[i] == -1:
            dfs(i, color, path, n, d)
            d += 1
    color = color[1:]
    color_cnt = Counter(color).values()
    print(max(color_cnt))



if __name__ == "__main__":
    main()