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

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
#define rep3(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define rep2(i, a, b) rep3(i, a, b, 1)
#define rep1(i, n) rep2(i, 0, n)
#define rep0(n) rep1(aaaaa, n)
#define ov4(a, b, c, d, name, ...) name
#define rep(...) ov4(__VA_ARGS__, rep3, rep2, rep1, rep0)(__VA_ARGS__)
#define per(i, a, b) for (ll i = (a) - 1; i >= (b); i--)
#define fore(e, v) for (auto &&e : v)
#define all(a) begin(a), end(a)
#define sz(a) (int)(size(a))
#define lb(v, x) (lower_bound(all(v), x) - begin(v))
#define eb emplace_back

template <typename T, typename S> bool chmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> bool chmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
const int INF = 1e9 + 100;
const ll INFL = 3e18 + 100;
#define i128 __int128_t
struct _ {
  _() { cin.tie(0)->sync_with_stdio(0), cout.tie(0); }
} __;

template <class T> vector<int> get_palindrome(const vector<T> &A) {
  vector<int> ret(A.size());
  int i = 0, j = 0;
  while (i < A.size()) {
    while (i - j >= 0 && i + j < A.size() && A[i - j] == A[i + j])
      j += 1;
    ret[i] = j;
    int k = 1;
    while (i - k >= 0 && k + ret[i - k] < j)
      ret[i + k] = ret[i - k], k += 1;
    i += k, j -= k;
  }
  return ret;
}

int main() {
  int N;
  cin >> N;
  vi A(N);
  fore(i, A) cin >> i;
  vi D;
  D.reserve(N * 2);
  D.push_back(0);
  rep(i, N - 1) {
    D.push_back(A[i + 1] - A[i]);
    D.push_back(0);
  }
  auto dz = get_palindrome(D);
  ll ans = 1;
  rep(i, N - 1) {
    ans += dz[i * 2 + 1] / 2;
    ans += (dz[i * 2] + 1) / 2;
  }
  cout << ans << '\n';
}