#include <fstream>

#include <algorithm>

using namespace std;

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

 int n,i,s,sum=0,st,k, v[801];

int main()
{
    in>>n;
    for(i=1; i<=n; i++)
        in>>v[i];
    sort(v+1, v+n+1);
    for(i=1; i+2<=n; i++)
    {
        k=i+1;
        for(st=i+1; st<n; st++)
        {
            while(k<=n and v[i]+v[st]>=v[k])
                k++;
            if(k>st)
                sum+=k-st-1;
        }
    }

    out<<sum;
    return 0;
}