n = int(input()) a = list(map(int, input().split())) # 0的个数 1 2 3 ... 100 b = [0 for _ in range(101)] for i in range(n): b[a[i]] += 1 ans = 0 for i in range(99): s = b[i] + b[i + 1] + b[i + 2] ans = max(ans, s) print(ans)