#include<fstream>
using namespace std;
int main ()
{
   ifstream fin("nrtri.in");
   ofstream fout("nrtri.out");
   int i,n,v[805],p,a,b,c,k;
    fin>>n;
    k=0;
    for(i=3;i<n+3;i++) fin>>v[i];
    for(a=3;a<n+1;a++)
    {
        for(b=a+1;b<n+2;b++)
        {
            for(c=b+1;c<n+3;c++)
            {
                if(v[a]<=v[b]+v[c] && v[b]<=v[a]+v[c] && v[c]<=v[a]+v[b])
                {
                    k++;
                }
                    else break;
            }
        }
    }
    fout<<k;

}