#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
ifstream cin("nrtri.in");
ofstream cout("nrtri.out");
int main()
{
    int n,i,j,s=0,x,cnt=0,val;
    cin>>n;
    vector <int>v(n+1);
    for (i=1;i<=n;i++)
    {
        cin>>v[i];
    }
    sort (v.begin(),v.end());
    for(i=1;i<=n-2;++i){
        for (j=i+1;j<=n-1;j++)
    {
        s=v[i]+v[j];
     auto it= upper_bound(v.begin()+j+1,v.end(),s);
     val=distance(v.begin()+j+1,it);
     cnt+=val;
    }}
    cout<<cnt<<'\n';
    return 0;
}