cf B. The Fibonacci Segment

http://codeforces.com/contest/365/problem/B

#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxn 200010
#define LL __int64
using namespace std;

int n;
LL a[maxn];

int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        for(int i=1; i<=n; i++)
        {
            scanf("%I64d",&a[i]);
        }
        int max1=min(2,n);
        int len=2;
        for(int i=3; i<=n; i++)
        {
            if(a[i]==a[i-2]+a[i-1])
            {
                len++;
                max1=max(max1,len);
            }
            else len=2;
        }
        printf("%d
",max1);
    }
    return 0;
}