from itertools import groupby



n = input()
a = [int(x) for x in input().split()]
g = [(x[0],len(list(x[1]))) for x in groupby(sorted(a))]


best = -1

for i in range(len(g)):
    best = max(best, g[i][1])
    if (i > 0) and (abs(g[i][0] - g[i-1][0]) < 1):
        best = max(best, g[i][1]+g[i-1][1])
    if (i < len(g)-1) and (abs(g[i][0] - g[i+1][0]) <= 1):
        best = max(best, g[i][1]+g[i+1][1])


print(best)