#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int v[801],n,sum;

int caut_bin(int x,int m)
{
    int pas=1<<10,i=0;
    while (pas!=0) {
        if (x>=v[i+pas+m] && i+pas+m<n) i+=pas;
        pas/=2;
    }
    return i-1;
}

int main()
{
    fin>>n;
    int x;
    for (int i=1;i<=n;i++) fin>>v[i];
    sort(v+1,v+n+1);
    for (int i=1;i<=n;i++) {
        for (int j=i+1;j<=n;j++) {
            x=v[i]+v[j];
            sum+=caut_bin(x,i);
        }
    }
    fout<<sum;
}