import bisect

n = int(input())
A = [int(input()) for _ in range(n)]
A.sort()

sorted_list = []
for x in A:
    # Find the rightmost value <= x-2
    idx = bisect.bisect_right(sorted_list, x - 2)
    if idx > 0:
        del sorted_list[idx - 1]
    bisect.insort(sorted_list, x)

print(len(sorted_list))