#include<cstdio>
const int N=100005;
int n,rez,a[N];
int main()
{
    freopen("numarare.in","r",stdin);
    freopen("numarare.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    for(int pi=1;pi<=n;pi++)
    {
        int pf=pi+1;
        for(int k=1;pi-k+1>0 && pf+k-1<=n;k++)
            if(a[pi-k]+a[pf+k]!=a[pi]+a[pf] || pi-k==0 || pf+k==n+1)
            {
                rez+=k;
                break;
            }
    }
    printf("%d",rez);
    return 0;
}