#include <bits/stdc++.h>

using namespace std;

using LL = long long;
#define endl '\n'
using db = double;
template <class T>
using max_heap = priority_queue<T>;
template <class T>
using min_heap = priority_queue<T, vector<T>, greater<T>>;

vector<int> manacher(vector<LL> &s)
{
    int n = s.size();
    vector<int> d1(n);
    for (int i = 0, l = 0, r = -1; i < n; i++)
    {
        // cerr << "i = " << i << " l = " << l << " r = " << r << endl;
        int k = (i > r) ? 1 : min(d1[l + r - i], r - i + 1);
        while (0 <= i - k && i + k < n && s[i - k] == s[i + k])
        {
            k++;
        }
        d1[i] = k--;
        if (i + k > r)
        {
            l = i - k;
            r = i + k;
        }
    }
    return d1;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;
    assert(n >= 1);
    assert(n <= 1e6);

    vector<LL> a(n);
    for (int i = 0; i < n; ++i)
    {
        cin >> a[i];
        assert(1 <= a[i] && a[i] <= 1e9);
    }

    vector<LL> B(n * 2, 1e18);
    for (int i = 1; i < n; ++i)
    {
        B[i * 2 - 2] = a[i] - a[i - 1];
    }

    LL ans = 0;
    auto ma = manacher(B);
    for (int i = 0; i < n * 2 - 3; i += 2)
        ans += (ma[i] + 1) / 2;
    for (int i = 1; i < n * 2 - 3; i += 2)
        ans += (ma[i]) / 2;

    cout << ans + n << endl;

    return 0;
}