#include <fstream>
using namespace std;
ifstream in("numarare.in");
ofstream out("numarare.out");
int n,a[100001],d[100001],st,dr,r;
int main()
{ in>>n;
  for(int i=1;i<=n;i++)
    in>>a[i];
  for(int i=1;i<n;i++)
    d[i]=a[i+1]-a[i];
  for(int i=1;i<=n;i++)
  { st=dr=i;
    while(d[st]==d[dr] && st>0 && dr<n)
      st--,dr++,r++;
  }
  out<<r;
  in.close();
  out.close();
  return 0;
}