n = int(input()) a = list(map(int, input().split())) b = [0 for _ in range(max(a) + 3)] for x in a: b[x] += 1 max_val = 0 for i in range(max(a) + 1): val = b[i] + b[i + 1] + b[i + 2] max_val = max(max_val, val) print(max_val)