from collections import Counter, defaultdict, deque

n = int(input())
ary = [None] * n
for i in range(n):
    ary[i] = (int(input()))

c = Counter(ary)

ks = sorted(c.keys())

result = 1
for i in range(len(ks) - 1):
    if ks[i + 1] - ks[i] == 1:
        if c[ks[i + 1]] + c[ks[i]]> result:
            result = c[ks[i + 1]] + c[ks[i]]

print(result)