#include <iostream>
#include <fstream>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int main()
{
    int n,nr=0;
    cin>>n;
    int v[n];
    for(int i=0;i<n;i++)
        cin>>v[i];
    for (int i = 0; i < n; ++i){
        for (int j = i+1; j < n; ++j) {
            if (v[i] > v[j]) {
                int aux = v[i];
                v[i] = v[j];
                v[j] = aux;
            }
        }
    }

    for(int i=0;i<n;i++)
    {
        for(int j=i+1;j<n;j++)
        {
            int de_gasit = v[i]+v[j];
            int dreapta=n-1,stanga=j;
            while(dreapta>stanga+1)
            {
                int mij=(stanga+dreapta)/2;
                if(de_gasit>v[mij])
                    stanga=mij;
                if(de_gasit<=v[mij])
                    dreapta=mij;
            }

            if (v[stanga + 1]== v[i] + v[j])
                stanga++;
            nr=nr+stanga-j;
        }
    }
    cout<<nr;
    return 0;
}