#include <fstream>
#include <algorithm>

using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
const int  L=14;
int n , v[801] , x , y , i, j, nr;
int cautbin(int x, int y)
{
       int r = 0;
    int pas = 1 << L;
    while(pas != 0){
        if(r + pas <= n && v[r + pas] <= x + y)
            r += pas;
        pas /= 2;
    }
    return r;
}
int main()
{
    f >>  n;
    for(i = 1;i <= n;i++)
        f >> v[i];
    sort(v,v+n+1);
    for(i=1; i<=n-1; i++)
    {
        for(j=i+1; j<=n; j++)
            nr+=cautbin(v[i],v[j])-j;
    }
    g << nr;
    return 0;
}