#include <bits/stdc++.h>

using namespace std;

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

using ll = long long;

int main() {
  in.tie(NULL);
  out.tie(NULL);
  ios_base::sync_with_stdio(false);
  int n; in >> n;
  vector<int> v(n);
  for (int &x : v)
    in >> x;
  vector<int> pal(n);
  for (int i = 0; i < n - 1; i++)
    v[i] = v[i + 1] - v[i];
  int l = -1, r = -1;
  ll ans = 0;
  for (int i = 0; i < n - 1; i++) {
    if (i > r)
      pal[i] = 1;
    else
      pal[i] = min(r - i + 1, pal[l + r - i]);
    while (i - pal[i] >= 0 && i + pal[i] < n && v[i + pal[i]] == v[i - pal[i]])
      pal[i]++;
    pal[i]--;
    if (i + pal[i] > r) {
      r = i + pal[i];
      l = i - pal[i];
    }
    ans += (pal[i] + 1);
  }
  out << ans << "\n";
  return 0;
}