#include <bits/stdc++.h>

using namespace std;

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

int n;
int a[100005];
int v[100005];
int l[100005];

int main()
{
    fin>>n;
    for(int i=1; i<=n; i++)
        fin>>a[i];

    if(n==1)
    {
        fout<<"0\n";
        return 0;
    }

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

    long long ans=1;

    int c=1,r=1;
    for(int i=2; i<n; i++)
    {
        if(r>=i)
            l[i]=min(l[2*c-i],r-i);

        while(i+l[i]+1<=n && i-l[i]-1>=1 && v[i+l[i]+1]==v[i-l[i]-1])
            l[i]++;

        if(i+l[i]>r)
        {
            r=i+l[i];
            c=i;
        }

        ans+=l[i]+1;
    }

    fout<<ans<<"\n";

    return 0;
}