#include <bits/stdc++.h>

using namespace std;
int v[801];
int n;
int cautbin(int st,int dr,int x)
{
    if (x<v[st]) return 0;
    if (x>=v[dr]) return n;
    int mij,poz=0;
    while (st<=dr)
    {
        mij=(st+dr)/2;
        if (v[mij]<=x)
        {
            poz=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    return poz;
}
int main()
{
    ifstream in("nrtri.in");
    ofstream out("nrtri.out");
    in>>n;
    int i, j, s=0;
    for (i=1;i<=n;i++)
    {
        in>>v[i];
    }
    sort (v+1,v+n+1);
    for (i=1;i<=n-2;i++)
    {
        for (j=i+1;j<=n-1;j++)
        {
            int p = cautbin(j+1,n,v[j]+v[i]);
            s += (p - j);
        }
    }
    out<<s<<"\n";
    out.close();
    return 0;
}