#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
long n,v[803],i,s,j,nr;
long long t;
int comp(long a,long b)
{
    return a<b;
}
int main()
{
    f>>n;
    for (i=1;i<=n;i++)
        f>>v[i];
    sort(v+1,v+n+1,comp);
    for (i=1;i<=n-2;i++)
        for (j=i+1;j<n;j++)
        {
            s=v[i]+v[j];
            nr=upper_bound(v+1,v+n+1,s)-v-1;
            t+=nr-j;
        }
    g<<t;
    f.close();
    g.close();
    return 0;
}