#include <fstream>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,i,v[805],mid,p,u,sol,j;
int main(){
    fin>>n;
    for(i=1;i<=n;i++){
        fin>>v[i];
    }
    for(i=1;i<=n-2;i++){
        for(j=i+1;j<=n-1;j++){
            p=j;u=n;
            while(p<=u){
                mid=(p+u)/2;
                if(v[i]+v[j]>v[mid]){
                    u=mid-1;
                }
                else{
                    p=mid+1;
                }
            }
            sol=sol+p-j+1;
        }
    }
    fout<<sol/2<<"\n";



    return 0;
}