<filename>jp.atcoder/abc002/abc002_4/19015616.py
def readline():
    import sys

    return sys.stdin.buffer.readline().rstrip()


def read():
    import sys

    return sys.stdin.buffer.read()


def readline_ints():
    (*ints,) = map(
        int,
        readline().split(),
    )
    return ints


def read_ints():
    import numpy as np

    return np.fromstring(
        string=read().decode(),
        dtype=np.int64,
        sep=" ",
    )


def bit_count(n):
    cnt = 0
    while n:
        cnt += n & 1
        n >>= 1
    return cnt


import numpy as np


def solve(n: int, m: int, xy: np.ndarray) -> None:

    relations = [0] * n
    for x, y in xy:
        relations[x] |= 1 << y
        relations[y] |= 1 << x

    cnt = 0
    for s in range(1 << n):
        t = (1 << n) - 1
        for i in range(n):
            if ~s >> i & 1:
                continue
            t &= relations[i] | 1 << i
        if not s & t == s:
            continue
        cnt = max(cnt, bit_count(s))

    print(cnt)


def main():
    import numpy as np

    n, m = readline_ints()
    xy = read_ints().reshape(m, 2) - 1
    solve(n, m, xy)


if __name__ == "__main__":
    main()

<filename>jp.atcoder/abc002/abc002_4/19015616.py
def readline():
    import sys

    return sys.stdin.buffer.readline().rstrip()


def read():
    import sys

    return sys.stdin.buffer.read()


def readline_ints():
    (*ints,) = map(
        int,
        readline().split(),
    )
    return ints


def read_ints():
    import numpy as np

    return np.fromstring(
        string=read().decode(),
        dtype=np.int64,
        sep=" ",
    )


def bit_count(n):
    cnt = 0
    while n:
        cnt += n & 1
        n >>= 1
    return cnt


import numpy as np


def solve(n: int, m: int, xy: np.ndarray) -> None:

    relations = [0] * n
    for x, y in xy:
        relations[x] |= 1 << y
        relations[y] |= 1 << x

    cnt = 0
    for s in range(1 << n):
        t = (1 << n) - 1
        for i in range(n):
            if ~s >> i & 1:
                continue
            t &= relations[i] | 1 << i
        if not s & t == s:
            continue
        cnt = max(cnt, bit_count(s))

    print(cnt)


def main():
    import numpy as np

    n, m = readline_ints()
    xy = read_ints().reshape(m, 2) - 1
    solve(n, m, xy)


if __name__ == "__main__":
    main()
