#include <fstream>
#include <algorithm>
using namespace std;

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

int n, a[808];
int nrt;

int main()
{
    fin >> n;
    for ( int i = 1; i <= n; i++ )
        fin >> a[i];

    int k, cnt;
    for ( int i = 1; i <= n; i++ )
        for ( int j = i + 1; j <= n; j++ )
        {
            k = j + 1;
            cnt = 0;
            while ( a[i] + a[j] >= a[k] && k <= n )
                cnt++, k++;
            nrt += cnt;
        }
    fout << nrt;
    fin.close();
    fout.close();
    return 0;
}