#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int main()
{
	int rez,ls,li,j,i,mij,a[800],n;
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>a[i];
    sort(a+1,a+n+1);
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            li=j+1;
            ls=n;
            while(li<=ls)
            {
                mij=(li+ls)/2;
                if(a[mij]>a[i]+a[j])
                    ls=mij-1;
                else
                    li=mij+1;
            }
            rez=rez+ls-j;
        }
    }
    fout<<rez;
    return 0;
}