#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
template<typename T>
std::vector<int> manacher(const vector<T>& s) {
	std::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 main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n; cin >> n;
	vector<int>a(n), b(n - 1), c(2 * n - 3, INF);
	rep(i, n)cin >> a[i];
	rep(i, n - 1)b[i] = a[i + 1] - a[i];
	rep(i, n - 1)c[i * 2] = b[i];
	long long ans = n;
	auto mn = manacher(c);
	rep(i, mn.size()) {
		if (i % 2 == 0) ans += (mn[i] + 1) / 2;
		else ans += (mn[i] + 0) / 2;
	}
	cout << ans << endl;
	return 0;
}