#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
vector <int> v;
int n;
int cautare(int a,int b)
{
    int r=n,st=b+1,m,val=v[a]+v[b];
    while(st<=r)
    {
        m=(st+r)/2;
        if (val<v[m])
        r=m-1;
        else st=m+1;
    }
    return r-b;
}

int main()
{
    int i,j,k,s=0,x;
    fin>>n;
    for(i=1;i<=n;i++)
    {
        fin>>x;
        v.push_back(x);
    }
    sort(v.begin(),v.end());
    for(i=0;i<n-2;i++)
        for(j=i+1;j<n-1;j++)
    {
      s=s+cautare(i,j);

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