#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,v[801],st,dr,mij,i,j,a,b,nrtri=0,ind;
    cin>>n;
    for (i=1; i<=n; i++)
        cin>>v[i];
    sort(v+1,v+n+1);
    for (i=1; i<=n; i++)
    {
        for (j=i+1; j<=n; j++)
        {
            a=v[i];
            b=v[j];
            st=j;
            dr=n;
            ind=-1;
            while (st<=dr)
            {
                mij=(st+dr)/2;
                if (v[mij] >a+b)
                    dr=mij-1;
                else
                {
                    ind=mij;
                    st=mij+1;
                }
            }
            nrtri+=ind-j;
        }
    }
    cout<<nrtri;
    return 0;
}