#include <bits/stdc++.h>
using namespace std;

using ll = long long;

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

int main(void) {
	int N;
	cin >> N;
	vector<int> A(N);
	for(int i = 0; i < N; ++i) cin >> A[i];
	
	if(N == 1) {
		cout << 1 << "\n";
		return 0;
	}
	
	const int M = 2 * N - 3;
	vector<int> B(M, INT_MAX);
	for(int i = 0; i < N - 1; ++i) B[i * 2] = A[i + 1] - A[i];
	
	vector<int> v = manacher(B);
	ll ans = 0;
	for(int i = 0; i < M; i += 2) ans += (v[i] + 1) / 2;
	for(int i = 1; i < M; i += 2) ans += v[i] / 2;
	
	cout << ans + N << "\n";
	return 0;
}