#include <iostream>
#include <fstream>
using namespace std;
const int NMAX=800;
int v[NMAX],n;
int nrtri(int n)
{
    int st,dr,ans=0;
    for(int i=0;i<n-2;i++)
    {
        st=i+1;
        dr=i+1;
        while(st<n-1)
        {
            while(dr<n-1 && v[i]+v[st]>=v[dr+1])
                dr++;;
            ans+=(dr-st);
            st++;

        }
    }
    return ans;
}
int main()
{
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");
    fin>>n;
    int aux;
    for(int i=0;i<n;i++)
    {
        fin>>v[i];
    }
    bool ilovesort=0;
    while(!ilovesort)
    {
        ilovesort=1;
        for(int i=0;i<n-1;i++)
        {
            if(v[i]>v[i+1])
            {
               aux=v[i];
               v[i]=v[i+1];
               v[i+1]=aux;
               ilovesort=0;
            }
        }
    }
    fout<<nrtri(n);
    return 0;
}