#include <fstream>

using namespace std;

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

const int nmax=800;
int v[nmax+1];

int main () {
    int n;
    fin>>n;

    for (int i=1; i<=n; i++) {
        fin>>v[i];
    }

    int sol=0;
    for (int k=n; k>=3; k--) {
        int j=k, i=1;
        while (j>i) {
            while (j-1>i && v[i]+v[j-1]>=v[k]) {
                --j;
            }
            sol+=k-j;
            i++;
        }
    }

    fout<<sol<<"\n";

    return 0;
}