#include<bits/stdc++.h>
using namespace std;int main(){int N;cin>>N;vector<int>A(N);for(int i=0;i<N;i++){cin>>A[i];}int ans=1;for(int i=0;i<N-1;i++){int d=A[i+1]-A[i];for(int 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<<endl;}