#include <bits/stdc++.h>
using namespace std;int N,i,j,d;int main(){cin >> N;vector<int> A(N);for(i=0;i<N;i++){cin>>A[i];}int ans=1;for(i=0; i<N-1; i++){int d=A[i+1]-A[i];for(j=i+1;j<N;j++){if(A[j]-A[j-1]!=d)break;if(ans<j-i+1)ans=j-i+1;}}cout<<ans<<"\n";}