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 = 0 ; i < n; ++ i)
cin >> a[i];
int maxlen = 0;
if(n == 1) maxlen = 1;
else if(n == 2) maxlen = 2;
else{
maxlen = 2;
int l = 0, r =1;
for(int i = 2; i < n; ++ i){
if(a[i] == a[i-1] + a[i-2]){
r = i;
if(maxlen < r-l+1){
maxlen = r-l+1;
}
}
else{
l = i-1;
}
}
}
cout<<maxlen<<endl;
return 0;
}