#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int main()
{
    int n,i,j,mij,t=0,s,d;

    fin>>n;

    int v[n];

    for(i=0; i<n; i++)
    {
        fin>>v[i];
    }

    sort(v,v+n);

    for ( i=0; i<n; i++ )
        for ( j=i+1; j<n-1; j++ )
        {
            s = j + 1;
            d = n;
            while ( s <= d )
            {
                mij = ( s + d )/2;
                if ( v[i] + v[j] >= v[mij] )
                    s = mij + 1;
                else
                    d = mij - 1;
            }
            t = t + d - j;
        }

        fout<<t;

    return 0;
}