import sys
from sys import stdin

n = int(stdin.readline())
a = map(int, stdin.readline().strip().split(' '))
counts = [0] * 100
for e in a:
  counts[e] += 1
max_num = 2
for i in range(2, 100):
  max_num = max(max_num, counts[i] + counts[i - 1])
print max_num