#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
int main ( )
{
    int n,i,v[801],r,j,pas,s=0;
    ifstream in ("nrtri.in");
    ofstream out ("nrtri.out");
    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++)
        {
           r=j;
           pas=1<<9;
           while(pas!=0)
           {
                if(r+pas<=n && v[r+pas]<=v[i]+v[j])
                {
                    r+=pas;
                }
                pas/=2;
           }
           if(v[r]<=v[i]+v[j])
           {
                s+=r-j;
           }
        }
    }
    out<<s;
    return 0;
}