#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
const int L=16;
int n, v[801],s;

bool cmp(int x, int y){
    return x<y;
}
int cauta(int x){
    int pas=1<<L,r=0;
    while(pas!=0){
        if(r+pas<=n && v[r+pas]<=x)
            r+=pas;
        pas/=2;
    }
    return r;
}


int main()
{
    int contor=0,i,j,k;
    in>>n;
    for(i=1;i<=n;i++)
        in>>v[i];

    sort(v+1,v+n+1,cmp);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++){
            s=v[i]+v[j];
            k=cauta(s);
            if(k>j){
                //cout<<v[i]<<v[j]<<v[k]<<"\n";
                contor += k - j;
            }
        }
    out<<contor;
    return 0;
}