#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,s=2,*a,c=2;
    cin>>n;
    if(n<=2)cout<<n<<endl;else{
    a=new int[n];
    while(n--)cin>>a[n];
    while(a[2]){
        if(*a+a[2]==a[1]*2)c++;
        else s=max(s,c),c=2;
        a++;
    }
    cout<<max(s,c)<<endl;
}}