#include<fstream>
#include<vector>
#define dmax 100004
using namespace std;
ifstream in("numarare.in");
ofstream out("numarare.out");

int n,x[dmax];
long int sol;


int main()
{	int i,j,a,b;
	in>>n;
	for(i=1;i<=n;i++)
		in>>x[i];
	in.close();
	sol=n-1;
	for(i=2;i<n-1;i++)
	{	a=i-1;
		b=i+2;
		while(a>0 && b<=n && x[a]+x[b] == x[a+1]+x[b-1])
		{	sol++;
			a--;
			b++;
		}	
	}	
	out<<sol;
	out.close();
	return 0;
}