#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int N,v[801],nr;
int main()
{
    f>>N;
    for(int i=1;i<=N;++i)
        f>>v[i];
    sort(v+1,v+N+1);
    for(int i=1;i<N-1;++i)
        for(int j=i+1;j<N;++j){
            int st=j+1,dr=N,mij;
            while(st<=dr){
                mij=(st+dr)/2;
                if(v[i]+v[j]>=v[mij])st=mij+1;
                else dr=mij-1;
            }
            nr+=dr-j;
        }
    g<<nr;
    return 0;
}