n=int(input())
alis=list(map(int,input().split()))
xlis=dict()
for i in set(alis):
    xlis[i-1]=0
    xlis[i+1]=0
    xlis[i]=0
for i in alis:
    xlis[i-1]+=1
    xlis[i+1]+=1
    xlis[i]+=1
print(max(xlis.values()))