#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
const int maxn=805;
int v[maxn];
inline int caut_bin_1(int x,int n)
{
    int st=1;
    int dr=n;
    int mij;
    int ans = -1;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(v[mij]>x)
            dr=mij-1;
        else if(v[mij]<=x) {
            st = mij+1;
            ans = mij;
        }
    }
    return ans;
}
int main()
{
    int n;
    in>>n;
    for(int i=1;i<=n;i++)
        in>>v[i];
    sort(v+1,v+n+1);
    int rasp = 0;
    for(int i = 1 ; i <= n ; ++ i)
        for(int j = i + 1 ; j <= n ; ++ j)
        {
            int k = caut_bin_1(v[i] + v[j], n);
            if(k != -1)
                rasp = rasp + k - j;
        }
    out << rasp << '\n';
    return 0;
}