Buggy python submission (verdict: Runtime Error):
from sys import stdin
from collections import Counter


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    a_arr = list(map(int,_in[1].split(' ')))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    count = Counter(a_arr)
    cnt = 0
    keys = sorted(count.keys())
    for key in keys:
        _ = count[key]
        try:
            _ += count[key+1]
        try:
            _ += count[key-1]
        cnt = max(cnt,_)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)

Fixed submission:
from sys import stdin
from collections import Counter


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    a_arr = list(map(int,_in[1].split(' ')))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    count = Counter(a_arr)
    cnt = 0
    keys = sorted(count.keys())
    for key in keys:
        _ = count[key]
        try:
            _ += count[key+1]
        except:
            pass
        try:
            _ += count[key-1]
        except:
            pass
        cnt = max(cnt,_)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin
from collections import Counter


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    a_arr = list(map(int,_in[1].split(' ')))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    count = Counter(a_arr)
    cnt = 0
    keys = count.keys()
    for key in keys:
        _ = count[key]
        if key+1 in keys:
            _ += count[key+1]
        if key-1 in keys:
            _ += count[key-1]
        cnt = max(cnt,_)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)


Fixed submission:
from sys import stdin
from collections import Counter


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    a_arr = list(map(int,_in[1].split(' ')))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    count = Counter(a_arr)
    cnt = 0
    keys = sorted(count.keys())
    for key in keys:
        _ = count[key]
        try:
            _ += count[key+1]
        except:
            pass
        try:
            _ += count[key-1]
        except:
            pass
        cnt = max(cnt,_)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin
from collections import Counter


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    a_arr = list(map(int,_in[1].split(' ')))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    count = Counter(a_arr)
    cnt = 0
    for key in count.keys():
        _ = count[key]
        if key+1 in count.keys():
            _ += count[key+1]
        if key-1 in count.keys():
            _ += count[key-1]
        cnt = max(cnt,_)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)


Fixed submission:
from sys import stdin
from collections import Counter


if __name__ == "__main__":
    _in = [_.rstrip() for _ in stdin.readlines()]
    N = int(_in[0])  # type:int
    a_arr = list(map(int,_in[1].split(' ')))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    count = Counter(a_arr)
    cnt = 0
    keys = sorted(count.keys())
    for key in keys:
        _ = count[key]
        try:
            _ += count[key+1]
        except:
            pass
        try:
            _ += count[key-1]
        except:
            pass
        cnt = max(cnt,_)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(cnt)