N=int(input())
A=list(map(int,input().split()))

ANS=min(N,2)
now=2
for i in range(2,N):
    if A[i]-A[i-1]==A[i-1]-A[i-2]:
        now+=1
    else:
        now=2
    ANS=max(ANS,now)
print(ANS)