#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,v[805],i,j,s,p,u,m,ss;
int main()
{
    f>>n;
    for(i=1;i<=n;i++) f>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<n-1;i++)
    {
        for(j=i+1;j<n;j++)
        {
            s=v[i]+v[j];
            p=1;
            u=n;
            while(p<=u)
            {
                m=(p+u)/2;
                if(v[m]<=s) p=m+1;
                else u=u-1;
            }
            ss=ss+(u-j);
        }
    }
    g<<ss<<" ";
    return 0;
}