#include <bits/stdc++.h>
#define long long ll
using namespace std;

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

int cauta(const vector<int>&v,int st , int dr , int val){
    int rez = -1;
    int i = st;
while(st<=dr){
    int mij = st+(dr-st)/2;
if(v[mij]<=val){
    rez = mij;
st = mij+1;
} else {
dr=mij-1;
}
}
if(rez==-1) return 0;
else return (rez-i+1);
}

int main()
{
    int n;
    int cont = 0;
    fin>>n;
    vector<int>v(n);
    int suma;
for(int i=0;i<n;i++){
    fin >> v[i];
}
sort(v.begin(),v.end());


for (int i = 0; i < n - 2; i++) {
        for (int j = i + 1; j < n - 1; j++) {
        suma = v[i]+v[j];
       cont+=cauta(v,j+1,n-1,suma);
        }
    }
fout << cont;

    return 0;
}