#include <bits/stdc++.h>
#define maxim 100005
using namespace std;

ifstream f("numarare.in");
ofstream g("numarare.out");

long long make_man (int (&s)[maxim], int n)
{
    int r = 0, c = 0;
    long long ans = 0;
    int z[maxim];
    z[0] = 0;
    for (int i = 1; i <= n; ++ i)
    {
        int op = 2 * c - i + 1;
        if (i > r || z[op] >= r - i)
        {
            if (i > r)
                r = i;
            int k = r + 1;
            int sum = s[k] +  s[2 * i - k + 1];
            while (k <= n && (2 * i - k + 1 >= 1) &&  s[k] + s[2 * i - k + 1] == sum)
                k ++;
            k --;
            z[i] = k - i;
            if (k > r)
            {
                c = i;
                r = k;
            }
        }
        else
            z[i] = z[op];
        ans += z[i];
    }
    return ans;
}

int main()
{
   int n;
   int s[maxim];
   f >> n;
   assert(n < maxim);
   for (int i = 1; i <= n; ++ i)
       f >> s[i];
   g << make_man(s, n);
}