#line 1 "g.cpp"
#include <bits/stdc++.h>
using namespace std;
using ll=long long;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}

#line 4 "/Users/Shared/po167_library/string/Manacher.hpp"


// https://snuke.hatenablog.com/entry/2014/12/02/235837
namespace po167{
template<class T>

// input  : abaab
// output : 1 0 3 0 1 4 1 0 1
std::vector<int> Manacher(std::vector<T> &v){
    int N = v.size();
    std::vector<int> res(N * 2 + 1);
    int i = 0, j = 0;
    while (i < N * 2 + 1){
        while (i - j >= 0 && i + j < N * 2 + 1 
            && (((i + j) & 1) == 0 || v[(i - j) / 2] == v[(i + j) / 2])) j++;
        res[i] = j;
        int k = 1;
        while (i - k >= 0 && k + res[i - k] < j) res[i + k] = res[i - k], k++;
        i += k, j -= k;
    }
    res.pop_back();
    res.erase(res.begin());
    for (auto &x : res) x--;
    return res;
}

// input  : abaab
// output : 1 0 3 0 1 4 1 0 1
std::vector<int> Manacher(std::string &s){
    std::vector<int> v(s.size());
    for (int i = 0; i < (int)s.size(); i++) v[i] = s[i];
    return Manacher(v);
}
}
#line 26 "g.cpp"

void solve();
// POP'N ROLL MUSIC / TOMOO
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    int N;
    cin >> N;
    vector<ll> A(N);
    rep(i, 0, N) cin >> A[i];
    if (N == 1){
        cout << "1\n";
        return;
    }
    vector<ll> D(N - 1);
    rep(i, 0, N - 1) D[i] = A[i + 1] - A[i];
    auto X = po167::Manacher(D);
    ll ans = 0;
    rep(i, 0, X.size()){
        ans += X[i] / 2;
    }
    ans += N * 2 - 1;
    cout << ans << "\n";
}