#include <fstream>
#include <algorithm>

using namespace std;

int step,start,n,i,v[805],j,nr,k;

int cautbin(int x)
{
    int start=j;
    int step=1;
    for(;step<=n;step<<=1);
    for(;step;step>>=1)
    {
        int index=start+step;
        if(index>n) continue;
        if(v[index]<=x)
            start=index;
    }
    return start;
}

int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i];
    sort(v,v+n+1);
    for(i=1;i<n;i++)
        for(j=i+1;j<=n;j++)
        {
        nr=v[i]+v[j];
        k=k+cautbin(nr)-j;
        }
    g<<k;
}