import sys


n = input()
a = map(int,sys.stdin.readline().split())
s=list(set(a))
i=0
c=0
while i<len(s)-1:
    if abs(s[i]-s[i+1])==1:
        
        if c<a.count(s[i])+a.count(s[i+1]):
            c=a.count(s[i])+a.count(s[i+1])
    elif c<a.count(s[i]):
        c=a.count(s[i])
    i+=1
if c<a.count(s[len(s)-1]):
    c=a.count(s[len(s)-1])
print c