#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("nrtri.in");
ofstream fout ("nrtri.out");


int n, v[809];
int sol, k;
int main()
{
    fin>>n;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    sort(v+1, v+1+n);
    for(int i=1; i<n-1; i++)
        for(int j=i+1; j<n; j++)
        {
            int st=j+1, dr=n;
            while(st<=dr)
            {
                int mid=(st+dr)/2;
                if(v[i]+v[j]>=v[mid])
                    st=mid+1;
                else
                    dr=mid-1;
            }
            sol+=(j-dr);
        }


    fout<<sol;




    return 0;

}