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