#include <iostream>
#include <fstream.h>

using namespace std;

int n, v[100000], i, j, k, s, contor = 0;
bool ok;

int main()
{
	ifstream f ("numarare.in");
	ofstream g ("numarare.out");
	
	f >> n;
	
	for (i = 0; i < n; i ++)
		f >> v[i];
	
	contor += n - 1;
	
	for(i = 4; i <= n; i += 2)
	{
		for(j = 0; j <= n - i; j ++)
		{
			ok = true;
			s = v[j] + v[j + i - 1];
			for(k = 1; k < i / 2; k ++)
			{
				if(!(v[j + k] + v[j  + i - k - 1] == s))
				{
					ok = false;
					break;
				}
			}
			if(ok)
				contor ++;
		}
	}//S[i+K-1] + S[j-K+1] 
	
	g << contor;
	
	f.close();
	g.close();
}