#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

vector<int> kai(vector<int> &s)
{
  int n = s.size(), c = 0;
  vector<int> ret(n);
  for (int i = 0; i < n; ++i)
  {
    int l = 2 * c - i;
    if (l >= 0 && c + ret[c] > i + ret[l]) ret[i] = ret[l];
    else
    {
      int j = c + ret[c] - i;
      while (i - j >= 0 && i + j < n && s[i - j] == s[i + j]) ++j;
      ret[i] = j;
      c = i;
    }
  }
  return ret;
}

int main()
{
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; ++i) cin >> a[i];
  vector<int> d(2 * n - 1);
  for (int i = 0; i < n - 1; ++i) d[i * 2 + 1] = a[i + 1] - a[i];
  auto res = kai(d);
  long long ans = 0;
  for (int i = 0; i < 2 * n - 1; ++i) ans += (res[i] + 1) / 2;
  cout << ans << endl;
}