#import<bits/stdc++.h>
using namespace std;int N,a=1,i,j,k,d;main(){cin>>N;int A[N];for(;k<N;k++)cin>>A[k];for(;i<N;d=A[++i]-A[i-1])for(j=i;j<N;a=max(a,j++-i+2))if(A[j]-A[j-1]-d)break;cout<<a;}