#include<fstream>
#include<algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,nr,p,k,i,j;
int v[801];
int main(){
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++){
        for(j=i+1;j<=n-1;j++){
                p=1<<16;
                k=0;
                while(p!=0) {
                    if(k+p<=n&&v[k+p]<=v[i]+v[j]) {
                        k+=p;
                    }
                    p/=2;
                }
                if(k>j){
                    nr+=k-j;
            }
        }
    }
    fout<<nr;
    return 0;
}