#include <fstream>
#include <algorithm>
using namespace std;
ifstream in ("nrtri.in");
ofstream out ("nrtri.out");
int v[900];
int main()
{
    int n,i,j,pas,r,s=0;
    in>>n;
    for(i=1;i<=n;i++)
        in>>v[i];

    sort(v+1,v+n+1);
    for(i=1;i<n-1;i++)
    {
        for(j=i+1;j<n;j++)
        {
            r=j;
            pas=1<<10;
            while(pas)
            {
                if(r+pas<=n && v[r+pas]<=v[i]+v[j])
                {
                    r+=pas;
                }
                pas/=2;
            }
            s+=r-j;
        }
    }
    out<<s;
    return 0;
}