#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int a[801],i,n,tri,k,j;
int main(){
    f>>n;
    for(i=1;i<=n;i++)
        f>>a[i];
    for(i=1;i<n-1;i++)
        for(j=i+1;j<n;j++)
            for(k=j+1;k<=n;k++)
                if(a[i]+a[j]>=a[k])
                    tri++;
                else
                    break;
    g<<tri;
    return 0;}