#include <bits/stdc++.h>
#define MAX 1000000
#define MIN -1000000
using namespace std;

ifstream fin("numarare.in");
ofstream fout("numarare.out");

int N;

int v[100005], a[100005];
int Pal[100005];

int main()
{
    fin >> N;

    for(int i = 1; i <= N; i++)
        fin >> v[i];

    for(int i = 1; i <= N - 1; i++)
        a[i] = v[i + 1] - v[i];

    a[N] = MAX;
    a[0] = MIN;

    int C, R;

    C = R = 0;

    for(int i = 1; i <= N - 1; i++)
    {
        int mirr = 2 * C - i;

        if(i < R)
            Pal[i] = min(Pal[mirr], R - i);

        while(a[i - Pal[i] - 1] == a[i + Pal[i] + 1])
            Pal[i]++;

        if(i + Pal[i] > R)
        {
            C = i;
            R = i + Pal[i];
        }
    }

    long long ans = 0;

    for(int i = 1; i <= N - 1; i++)
        ans += (long long)(Pal[i] + 1);

    fout << ans;

    return 0;
}