#include <bits/stdc++.h>

using namespace std;
ifstream fin("numarare.in");
ofstream fout("numarare.out");
int n, a[100005];
long long sol;

int main()
{
    int i, st, dr;
    fin >> n;
    for(i = 1;i <= n;i++)
        fin >> a[i];
    for(i = 1;i < n;i++)
    {
        st = i - 1;
        dr = i + 2;
        while(st >= 1 && dr <= n && a[st] - a[st + 1] + a[dr] - a[dr - 1] == 0)
        {
            st--;
            dr++;
        }
        sol += (i - st);
    }
    fout << sol << "\n";
    fout.close();
    return 0;
}