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

        }
    }
    out<<cnt;
    return 0;
}