#include<fstream>
#include<algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,i,j,x,sol,st,dr,mid;
int v[805];
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++){
            st=j+1;
            dr=n;
            while(st<=dr){
                mid=(st+dr)/2;
                if(v[mid]>v[i]+v[j])
                    dr=mid-1;
                else
                    st=mid+1;
            }
            if(dr>j){
                sol+=(dr-j);
            }
        }
    }
    fout<<sol;
    return 0;
}