#!/usr/bin/python
"""
3542.cc:  No.3542 Progression (Python) - yukicoder
"""

# main

def main():
    n = int(input())
    a = list(map(int, input().split()))

    if n <= 2:
        print(n)
        return

    b = [0] * (n - 1)
    for i in range(0, n - 1):
        b[i] = a[i + 1] - a[i]

    i = 0
    maxl = 0
    while i < n - 1:
        j = i
        while i < n - 1 and b[j] == b[i]:
            i += 1
        maxl = max(maxl, i - j + 1)

    print(maxl)

main()