#include<fstream>
#include<algorithm>

using namespace std;

int n, a[810], nr;
 int i,j,k;
int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f>>n;
    for(i=1;i<=n;i++)
        f>>a[i];

    sort (a+1, a+n+1);

    for (i=1;i<=n-2;i++)
        for (j=i+1;j<=n-1;j++)
            for (k=j+1;k<=n&&a[i]+a[j]>=a[k];k++)
                nr++;
    g<<nr<<'\n';


    return 0;
}