from collections import Counter

n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]

c = Counter(a)
ans = 0
for i, j in zip(sorted(c), sorted(c)[1:]):
    tmp = c[i] + c[j]
    if j - i == 1 and tmp > ans:
        ans = tmp
print(max(ans, max(c.values())))