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