#include <bits/stdc++.h>
#pragma GCC target("avx2")
/*
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
*/
#pragma GCC target("prefer-vector-width=512")
#pragma GCC optimize("Ofast,unroll-loops")

using namespace std;
using i32 = int;
using i64 = long long;
using f32 = float;
using f64 = double;
using f80 = long double;

#define rep(i, n) for(i64 i = 0; i < (n); i++)
#define all(x) (x).begin(), (x).end()

template<class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p);
template<class T>
ostream& operator<<(ostream& os, const vector<T>& v);

template<class T, class U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << ", " << p.second << ")";
    return os;
}

template<class T>
istream& operator>>(istream& is, vector<T>& v) {
    for(int i = 0; i < (int)v.size(); i++) {
        is >> v[i];
    }
    return is;
}

template<class T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    for(int i = 0; i < (int)v.size(); i++) {
        if(i > 0) os << " ";
        os << v[i];
    }
    return os;
}

void YesNo(bool yn) {
    if(yn) cout << "Yes" << endl;
    else cout << "No" << endl;
}

void YesNoExit(bool yn) {
    YesNo(yn);
    exit(0);
}

template<class T, class U>
bool chmin(T &x, U y) {
    if(y < x) {
        x = y;
        return true;
    }
    return false;
}

template<class T, class U>
bool chmax(T &x, U y) {
    if(y > x) {
        x = y;
        return true;
    }
    return false;
}

struct UnionFind {
  vector<int> data;

  UnionFind() = default;

  explicit UnionFind(size_t sz) : data(sz, -1) {}

  bool unite(int x, int y) {
    x = find(x), y = find(y);
    if (x == y) return false;
    if (data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }

  int find(int k) {
    if (data[k] < 0) return (k);
    return data[k] = find(data[k]);
  }

  int size(int k) { return -data[find(k)]; }

  bool same(int x, int y) { return find(x) == find(y); }

  vector<vector<int> > groups() {
    int n = (int)data.size();
    vector<vector<int> > ret(n);
    for (int i = 0; i < n; i++) {
      ret[find(i)].emplace_back(i);
    }
    ret.erase(remove_if(begin(ret), end(ret),
                        [&](const vector<int>& v) { return v.empty(); }),
              end(ret));
    return ret;
  }
};

void out() { cout << '\n'; }
template <class T, class... Ts>
void out(const T& a, const Ts&... b) {
    cout << a;
    (cout << ... << (cout << ' ', b));
    cout << '\n';
}

vector<i32> dx4 = {0, 1, 0, -1};
vector<i32> dy4 = {1, 0, -1, 0};

const i64 MOD = 998244353;
const i32 i32_inf = 1e9;
const i64 i64_inf = 1e18;

struct Eratosthenes {
    int _n;
    vector<int> prv;
    Eratosthenes() {}
    Eratosthenes(int n) : _n(n + 1), prv(_n, 0) {
        prv[0] = -1;
        prv[1] = -1;
        for(int i = 2; i < _n; ++i) {
            if(prv[i]) continue;
            for(int k = 2; i * k < _n; ++k) {
                prv[i * k] = k;
            }
        }
    }

    bool isPrime(int x) {
        return prv[x] == 0;
    }

    vector<int> get(int x) {
        assert(2 <= x && x < _n);
        vector<int> ret;
        while(prv[x]) {
            ret.emplace_back(x / prv[x]);
            x = prv[x];
        }
        ret.emplace_back(x);
        return ret;
    }
};

vector< int > manachar(vector< long long >& 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] == 2 * s[i])) {
        ++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;
    j = max(j, 1);
  }
  return radius;
}

void solve() {
    // 構造がめちゃめちゃ回文なのでManacharみたいなことをしたいな～
    // 偶奇が異なるやつは適当な$相当なことをする

    i32 n; cin >> n;
    vector<i64> a(n); cin >> a;
    
    vector<i64> c(2 * n - 1);
    for(i32 i = 0; i < 2 * n - 1; ++i) {
        if(i % 2 == 0) c[i] = 2 * a[i/2];
        else c[i] = a[i/2] + a[i/2+1];
    }

    // out(c);

    i64 ans = 0;
    vector<i32> res = manachar(c);
    // out(res);
    for(int i = 0; i < 2 * n - 1; i++) {
        ans += (res[i] + 2) / 2;
    }
    out(ans - n + 1);
}

int main() {
    int TESTCASE = 1;
    // cin >> TESTCASE;
    while(TESTCASE--) {
        solve();
    }
}