#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int v[805],n,i,nr,k,j,p,u,ok,mij,a,x;
int main()
{fin>>n;
for (i=1;i<=n;i++)
{
    fin>>v[i];
}
nr=0;
sort (v+1,v+n+1);
for (i=1;i<=n;i++)
{
    for (j=i+1;j<=n;j++)
    {
        p=j+1;u=n;
        x=v[i]+v[j];
        ok=0;
        while (p<=u&&ok==0)
        {
            mij=(p+u)/2;
            if (x>=v[mij]) {ok=mij;nr++;p=mij+1;}
            else if (x<v[mij]) u=mij-1;
            else p=mij+1;
        }
    }
}
fout<<nr;

    return 0;
}