#include <fstream>
#include <algorithm>
#include <vector>

using namespace std;

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

int main()
{
    int n;
    fin>>n;
    vector<long long>v(n);
    for (int i=0; i<n; i++){
        fin>>v[i];
    }
    sort(v.begin(), v.end());
    long long cnt=0;
    for(int k=n-1; k>=2; k--){
        int i=0, j=k-1;
        while(i<j){
            if(v[i]+v[j]>=v[k]){
                cnt+=(j-i);
                j--;
            }else{
                i++;
            }
        }
    }

    fout<<cnt<<endl;
    return 0;
}