d = {}
n = int(input())
l = list(map(int,input().split()))
for i in range(n):
  x = l[i]
  d[x] = d.get(x,0)+1
a = []
for i in d.items() :
  a.append(i)
mx = a[0][1]
for i in range(1,len(a)):
  mx = max(mx , a[i][1])
  ch = abs(a[i][0] - a[i-1][0])
  if ch <= 1 :
    mx = max(mx , a[i][1]+a[i-1][1])
print(mx)