#include <bits/stdc++.h>
using namespace std;
int main() { int N; cin >> N; vector<int> A(N);int i,j;for(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(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";}