#include <bits/stdc++.h>

using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,nr,a[801];

int main()
{
    f>>n;
    for(int i=1; i<=n; i++)
        f>>a[i];
    for(int i=1; i<=n-2; ++i)
        for(int j=i+1; j<=n-1; ++j)
        {
            int k=j+1;
            while(a[i]+a[j]>=a[k]&&k<=n)
                ++k;
            nr+=k-j-1;

        }
    g<<nr;
    return 0;
}