//https://ei1333.github.io/luzhiled/snippets/string/manacher.htmlを引用
#include <bits/stdc++.h>
using namespace std;
#define int long long

int INF = 1e18;

vector< int > manacher(vector<int> &s) {
  vector< int > radius(s.size());
  int i = 0, j = 0;
  while(i < s.size()) {
    while(i - j >= 0 && i + j < s.size() && s[i - j] == s[i + j]) {
      ++j;
    }
    radius[i] = j;
    int k = 1;
    while(i - k >= 0 && i + k < s.size() && k + radius[i - k] < j) {
      radius[i + k] = radius[i - k];
      ++k;
    }
    i += k;
    j -= k;
  }
  return radius;
}

int N;

signed main(){
    cin>>N;
    vector<int> A(N*2);
    vector<int> B(N*2-3,INF);
    for(int i = 0; i < N; i++){
    	cin>>A[i];
    	if(i >= 1) B[i*2-2] = A[i] - A[i-1];
    }
    vector<int> now = manacher(B);
    int ans = 0;
    for(int i = 0; i < N*2-3; i += 2) ans += (now[i]+1)/2;
    for(int i = 1; i < N*2-3; i += 2) ans += (now[i])/2;
    cout << ans + N << "\n";
}