#include<fstream>
#include<algorithm>
#define maxn 805

using namespace std;

ifstream f("nrtri.in");
ofstream g("nrtri.out");

int a[maxn],i,n,j,step,k,p;

int main()
{
    f>>n;

    for(i=1;i<=n;++i)
        f>>a[i];

    sort(a+1,a+n+1);

    for(i=1;i<n;++i,k=0)
        for(j=i+1;j<n;++j)
        {
            while(k<n&&a[i]+a[j]>=a[k+1])
                ++k;
            p+=k-j;
        }

    g<<p<<"\n";

    f.close();
    g.close();

    return 0;
}