import sys
from itertools import pairwise


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    n = int(input())
    a = sorted(int(input()) for _ in range(n))
    for x, y in pairwise(a):
        if y-x == 1:
            return 2

    return 1

if __name__ == '__main__':
    ret = main()
    if ret is not None:
        print(ret)