#include <fstream>
#include <cstdio>
#define VAL 100005

using namespace std;

int N, i, j;
int ANS, be, en;
int v[VAL], dif[VAL];

int main()
{
    freopen("numarare.in", "r", stdin);
    freopen("numarare.out", "w", stdout);
    scanf("%d", &N);
    for (i=1; i<=N; i++)
    {
        scanf("%d", &v[i]);
        dif[i-1]=v[i]-v[i-1];
    }
    for (i=1; i<N; i++)
    {
        be=en=i;
        while (1)
        {
            if (be==0 || en==N || dif[be]!=dif[en])
              break;
            else
            {
                ANS++;
                be--;
                en++;
            }
        }
    }
    printf("%d\n", ANS);
    return 0;
}