#include <fstream>
#include <cmath>

using namespace std;

ifstream fi("numarare.in");
ofstream fo("numarare.out");

int a[100005],n,sum,i,j,k,x,y;

int main()
{
   fi>>n;

   for(i=1;i<=n;i++)
     fi>>a[i];

   i=0;j=1;

   do{
    i++;j++;
    k++;
    sum=a[i]+a[j];
    x=i;
    y=j;
    while(x-1>=1 and y+1<=n
          and a[x-1]+a[y+1]==sum){
        x--;y++;k++;
    }


   }while(j<n);

   fo<<k;














    return 0;
}