#include<fstream>
#define InFile "nrtri.in"
#define OutFile "nrtri.out"
using namespace std;
int n,k,v[811],i,j,g;
int main()
{
    ifstream fin(InFile);
    ofstream fout(OutFile);
    fin>>n;
    for(i=1;i<=n;++i)fin>>v[i];
     for(i=1;i<=n-2;++i)
     for(j=i+1;j<=n-1;++j)
     for(g=j+1;g<=n&&v[i]+v[j]>=v[g];++g)
     k++;

fout<<k;
  return 0;
}