#include<fstream>
#include<algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int v[805],n,nr=0;

int main()
{
    int i,j,div,p,suma=0;
    in>>n;
    for(i=1;i<=n;i++)
        in>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            p=1<<9;
            div=j+1;
            while(p)
            {
                if(p+div<=n && v[p+div]<=v[i]+v[j])
                    div+=p;
                p/=2;
            }
            if(v[div]<=v[i]+v[j])
                suma+=div-j;
        }
    }
    out<<suma<<'\n';
    return 0;
}