#include <iostream>
#include <algorithm>
using namespace std;
int x,N,contor,r,l,i,v[801],j,n,nr;

int cautarebin(int x,int contor)
{
    int mijl,l=contor,r=N-1;
    mijl=(l+r)/2;
    while(l<=r)
    {
        if(x>=v[mijl])
            l+=1;
        if(x<=v[mijl])
            r-=1;
    }
    return r;

}

int main()
{
    cin>>N;
    for(int i=0; i<N; i++)
        cin>>v[i];
    sort(v,v+N);
    for(int i=0; i<N-1; i++)
    {
        for(int j=i+1; j<N; j++)
        {
            n=cautarebin(v[i]+v[j],j+1);
            nr+=n-j+1;
        }
    }
    cout<<nr;

    return 0;
}