#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

int main()
{
    ifstream fin("nrtri.in");ofstream fout("nrtri.out");
    int n,v[810],i,j,a,k,m=0;
    fin>>n;
    for(i=1;i<=n;i++) fin>>v[i];
    sort(a+1,a+n+1);
    for(i=1;i<n;i++) for(j=i+1;j<=n;j++)
    {
        k=j,a=i+j;
        while(a>0)
        {
            a=(a+1)/2;
            if(v[k+a]<v[i]+v[j]) k=k+a;
        }
        m=m+k-j;
    }
    fout<<m;
    return 0;
}