#include <iostream>
#include <algorithm>
#include<fstream>
using namespace std;
int v[801];
int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    int n, i, j,contor=0, k, s;
    f>>n;
    for(i=1;i<=n;i++) {f>>i;};
    sort(v+1,v+n+1);
    for(i=1;i<=n;i++){
        for(j=i+1;j<=n;j++){
            s=i+j;
        }
        int st=i;
        int dr=n;
        k=j;
        while(st<=dr){
            int med=(st+dr)/2;
            if(v[med]<=s){
                k=med;
                st=med+1;
            }
            else{
                dr=med-1;
            }
        }
        k=k-j;
        contor=contor+k;
    }
    g<<contor;

    return 0;
}