#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int sol,sol1,dr,st,j,i,mijl,v[801],n;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            st=j+1;
            dr=n;
            while(st<=dr)
            {
                mijl=(st+dr)/2;
                if(v[mijl]>v[i]+v[j])
                    dr=mijl-1;
                else
                    st=mijl+1;
            }
            sol=sol+dr-j;
        }
    }
    fout<<sol;
    return 0;
}