#include <fstream>
#include <algorithm>
#define In "nrtri.in"
#define Out "nrtri.out"
#define Nmax 805
using namespace std;
int a[Nmax],sol,n;
inline void Citire()
{
    ifstream f(In);
    f>>n;
    for(int i=1;i<=n;i++)
        f>>a[i];
    f.close();
    sort(a+1,a+n+1);
}
inline void Rezolvare()
{
    int i,j,k;
    for(i=1;i<=n-2;i++){
        for(j=i+1;j<=n-1;j++){
		k = max(k,j);
	while(k < n && a[i]+a[j] >= a[k+1])
		++k;
	sol += k-j;
}
}
}
inline void Afisare()
{
    ofstream g(Out);
    g<<sol<<"\n";
    g.close();
}
int main()
{
    Citire();
    Rezolvare();
    Afisare();
    return 0;
}