#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
int st,dr,m,v[850],n,i,j,k,sum=0,mod=0,x;
ifstream in("nrtri.in");
ofstream out("nrtri.out");

int main()
{
    in.sync_with_stdio(false);
    out.sync_with_stdio(false);
    in>>n;
    for(i=1;i<=n;i++)
        in>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
        {
            sum=v[i]+v[j];
            st=j;
            dr=n+1;
            while(dr-st!=1)
            {
                m=(st+dr)/2;
                if(v[m]<=sum)
                    st=m;
                else dr=m;
            }
            mod=mod+ st-j;
        }
    out<<mod;
    return 0;
}