n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]

counts = [0]*99
for num in a:
    counts[num-1] += 1

maxval = 2
for i in range(len(counts)-1):
    result = counts[i] + counts[i+1]
    if result > maxval:
        maxval = result
            
print(maxval)