#include <iostream>
#include <fstream>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
const int MAX = 800; //nr de elem. in vector
int n, v[MAX+1];
int cautbin (int i, int j)
{
    int st=j+1, dr=n, res=-1;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if( v[i]+v[j]>=v[mij] )
        {
            res=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    return res;
}
int main()
{
    in>>n;
    for(int i=1; i<=n; ++i)
        in>>v[i];
    int cnt=0;
    for(int i=1; i<=n; ++i)
    {
        for(int j=i+1; j<=n; ++j)
        {
           if( cautbin(i,j)!=-1 )
            cnt++;
//cout<<cautbin(i, j)<<'\n';
        }
    }
    out<<cnt;
    return 0;
}