#include <bits/stdc++.h>

using namespace std;

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

const int NMAX=801;

int v[NMAX],n;

int main()
{
    int rez=0,k;
    in>>n;
    for(int i=0;i<n;++i)
        in>>v[i];
    for(int i=0;i<n;++i)
        {
            k=i+1;
            for(int j=i+1;j<n;j++)
            {
                while(k<n && v[k]<=v[i]+v[j])
                {
                    k++;
                }
                if(k>j)
                {
                    rez+=k-j-1;
                }
            }
        }
    out<<rez;
    return 0;
}