#include <stdio.h>
#include <algorithm>

using namespace std;

#define maxn 100010

long n, i, j, k, lg, ras[maxn], sol, ok, v[maxn], pt[maxn];
long h1, h2;

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]);
    lg=2;
    for(i=1; i<n; i++)
    {
        for(j=1; v[i]+v[i+1]==v[i-j]+v[i+1+j]; ++j);
        sol+=j;
    }
    printf("%d\n", sol);
    return 0;
}