#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
int t[805];
int main()
{
    int N,i,j,k,st,dr,mid,poz,S=0;
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");
    fin>>N;
    for(i=1;i<=N;i++)
    {
        fin>>t[i];
    }
    sort(t+1,t+N+1);
    for(i=1;i<=N-2;i++)
    {
        for(j=i+1;j<=N-1;j++)
        {
            st=j+1;
            dr=N;
            while(st<=dr)
            {
                mid=(st+dr)/2;
                if(t[j]+t[i]>=t[mid])
                {
                    poz=mid;
                    st=mid+1;
                }
                else
                {
                    dr=mid-1;
                }
            }
            S=S+poz-j;
        }
    }
    fout<<S;
    return 0;

}