n = int(raw_input())
a = list(map(int, raw_input().split()))

a.sort()
maxim = 0

for i in xrange(1, n) :
    j = i-1
    count = 0
    while (j <= n-1 and a[j] - a[i-1] <= 1) :
        j = j + 1
        count = count + 1
    if count > maxim :
        maxim = count

print maxim