n=int(input().strip())
a=[int(a_temp) for a_temp in input().strip().split(' ')]
b=[0 for x in range(100)]
for x in a:
    b[x]+=1
ma=0
for x in range(99):
    k=b[x]+b[x+1]
    if k>ma:    ma=k    
print(ma)