#include<fstream>

using namespace std;

long int n,i,v[1000],j,k,aux;
int main()
{
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");
    fin>>n;
    for(i=1;i<=n;i++)
       fin>>v[i];
    for(i=1;i<=n;i++)
       for(j=i+1;j<=n;j++)
          if(v[i]<v[j])
            {
            v[i]=aux;
            v[i]=v[j];
            v[j]=aux;
            }
    for(i=1;i<=n;i+=2)
       {
       for(j=i+2;j<=n;j++)
          if(v[i]+v[i+1]>=v[j])
            k++;
       }
    fout<<k;
}