#include <fstream>
using namespace std;
ifstream fin ("numarare.in");
ofstream fout ("numarare.out");
int n,i,p,sum,v[100001],a[100001];

int main () {

    fin>>n>>v[1];
    for (i=2;i<=n;i++) {
        fin>>v[i];
        v[i-1]-=v[i];
    }
    sum=n-1; p=1;
    for (i=1;i<n;i++) {
        if (i<p+a[p]) {
            if (a[2*p-i]<=p+a[p]-i)
                a[i]=a[2*p-i];
            else
                a[i]=p+a[p]-i;
        }
        if (i+a[i]>=p+a[p]) {
            p=i;
            while ((i-a[i]-1>=1)&&(i+a[i]+1<=n)&&(v[i-a[i]-1]==v[i+a[i]+1]))
                a[i]++;
        }
    }
    for (i=1;i<n;i++)
        sum+=a[i];
    fout<<sum<<"\n";
    return 0;
}