#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    int n,i,j,cnt=0,aux;
    fin>>n;
    int v[n+1];
    for(i=1;i<=n;++i){
        fin>>v[i];
    }
    int dr,st,mijl;
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;++i){
        for(j=i+1;j<=n-1;++j){
            st=j;
            dr=n;
            aux=j;
            while(st<=dr){
                mijl=(st+dr)/2;
                if(v[mijl]>v[i]+v[j]){
                    dr=mijl-1;
                }
                else{
                    st=mijl+1;
                    aux=mijl;
                }
            }
            cnt=cnt+aux-j;
        }
    }
    fout<<cnt;
    return 0;
}