#include<fstream>
#include<iostream>
#include<algorithm>
#define NMax 807
#define LMax 30005
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int N,Sol;
int T[NMax];

void Read()
{
    fin>>N;

    for(int i=1;i<=N;++i)
        fin>>T[i];
}

void Solve()
{
    sort(T+1,T+N+1);


    for(int i=1;i<=N-2;++i)
        for(int j=i+1;j<=N-1;++j)
        {
            int k=j+1;
            while(T[i]+T[j]>=T[k] && k<=N)  k++;
            Sol+=k-j-1;
        }
}

void Print()
{
    fout<<Sol<<"\n";
}

int main()
{
    Read();
    Solve();
    Print();

    fin.close();
    fout.close();
    return 0;
}