#include <bits/stdc++.h>

using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int a[807],n;
void Citire()
{
    int i;
    f>>n;
    for(i=1;i<=n;i++)
        f>>a[i];
}
void Rez()
{
    int i,j,sol=0,contor=0;
    for(i=1;i<=n;i++)
        for(j=1+i;j<=n;j++)
        {
         contor=j+1;
         while(a[i]+a[j]>=a[contor] && contor<=n)
                contor++;
         sol+=contor-(j+1);
        }
    g<<sol<<"\n";
}
int main()
{
    Citire();
    Rez();
    return 0;
}