#include <fstream>

using namespace std;

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

int n;
long long sol;

int v[100005], dp[100005];

int main() {
  cin >> n;
  for(int i = 1; i <= n; i++) {
    cin >> v[i];
    v[i] -= v[i - 1];
  }
  int l = 1, r = 1;
  sol = n;
  for(int i = 1; i <= n; i++) {
    if(i > r)
      l = r = i;
    else
      dp[i] = min(dp[l + r - i], r - i);
    if(i > r && dp[i] != r - i)
      continue;
    l = i - dp[i]; r = i + dp[i];
    while(r <= n && l && v[l] == v[r])
      l--, r++;
    l++, r--;
    dp[i] = (r - l + 1) / 2;
    sol += dp[i];
  }
  cout << sol;
  return 0;
}