Codeforces Round #213 (Div. 2) B. The Fibonacci Segment

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(int i =  ; i < n; ++ i)
        cin >> a[i];
    int maxlen = ;
    if(n == ) maxlen = ;
    else if(n == ) maxlen = ;
    else{
        maxlen = ;
        int l = , r =;
        for(int i = ; i < n; ++ i){
            if(a[i] == a[i-] + a[i-]){
                r = i;
                if(maxlen < r-l+){
                    maxlen = r-l+;
                }
            }
            else{
                l = i-;
            }
        }
    }
    cout<<maxlen<<endl;
    return ;
}