#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("nrtri.in");
ofstream fout ("nrtri.out");
int v[801],i,j,p,u,mij,s,sum,n;
int main () {

    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];
    sort (v+1,v+n+1);
    for (i=1;i<=n-2;i++)
        for (j=i+1;j<=n-1;j++){
            s=v[i]+v[j];
            p=1;u=n;
            while (p<=u){
                mij=(p+u)/2;
                if (v[mij]<=s)
                    p=mij+1;
                else
                    u=mij-1;
            }
            sum+=p-j-1;
        }
    fout<<sum<<"\n";

    return 0;
}