#include <fstream>
#include <vector>
using namespace std;

ifstream f("nrtri.in");
ofstream g("nrtri.out");

int v[801];

int binarySearch(int value, int n) {
    int pos = 0;
    for (int p = 20; p >= 0; --p) {
        if (pos + (1 << p) <= n && v[pos + (1 << p)] <= value) {
            pos += (1 << p);
        }
    }
    return pos;
}

int main() {
    int n, cont=0;
    f>>n;
    for(int i = 1; i<=n; i++){
        f>>v[i];
    }
    for(int i = 1; i<n; i++){
        for(int j = i+1; j<=n; j++){
            if(v[i]>v[j]){
                swap(v[i], v[j]);
            }
        }
    }
    for(int i = 1; i<n; i++){
        for(int j = i+1; j<=n; j++){
            int value = v[i]+v[j];
            cont += binarySearch(value, n)-j;
        }
    }
    g<<cont;
    return 0;
}