#include <iostream>
#include <fstream>

using namespace std;
const int NMAX=800;
int v[NMAX+1],n;
int nrtri(int n)
{
    int dr,st,ans=0;
    for(int i=1;i<=n-2;i++)
    {
        st=i+1;
        dr=i+1;
        while(st<=n-1)
        {
            while(dr<n && v[i]+v[st]>=v[dr+1])
            {
                dr++;
            }
            ans+=(dr-st);
            st++;
        }
    }
    return ans;
}
int main()
{
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");

    int n,aux;
    fin>>n;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    bool sortat=0;
    while(!sortat)
    {
        sortat=1;
        for(int i=1;i<n;i++)
        {
            if(v[i]>v[i+1])
            {
                aux=v[i];
                v[i]=v[i+1];
                v[i+1]=aux;
                sortat=0;
            }
        }
    }
    fout<<nrtri(n);
    return 0;
}