#include <fstream>
#include <vector>
#include <bitset>

using namespace std;

const char infile[] = "numarare.in";
const char outfile[] = "numarare.out";

ifstream fin(infile);
ofstream fout(outfile);

const int MAXN = 100005;
const int oo = 0x3f3f3f3f;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

const inline int min(const int &a, const int &b) { if( a > b ) return b;   return a; }
const inline int max(const int &a, const int &b) { if( a < b ) return b;   return a; }
const inline void Get_min(int &a, const int b)    { if( a > b ) a = b; }
const inline void Get_max(int &a, const int b)    { if( a < b ) a = b; }

int N, A[MAXN], P[MAXN];
long long Ans;

inline void manacherAlgorithm(void) {
    int center = 0, best = 0;
    for(int i = 1 ; i < N ; ++ i) {
        if(i < best)
            P[i] = min(P[2*center - i], best - i - 1);
        while(i - P[i] > 0 && i + P[i] + 1 <= N && A[i - P[i]] + A[i + P[i] + 1] == A[i] + A[i + 1])
            ++ P[i];
        if(i + P[i] + 1 > best) {
            best = i + P[i];
            center = i;
        }
        Ans += 1LL * P[i];
    }
}

int main() {
    fin >> N;
    for(int i = 1 ; i <= N ; ++ i)
        fin >> A[i];
    manacherAlgorithm();
    fout << Ans << "\n";
    fin.close();
    fout.close();
    return 0;
}