#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int n,i,j,v[801],nr,x,y,mij,p1,p2;
int div1(int p,int q){
if(p==q)return p;
else {mij=(p+q)/2;
    if(x<=v[mij])div1(p,mij);
    else div1(mij+1,q);
}
}
int div2(int p,int q){
if(p==q)return p;
else {mij=(p+q)/2;
    if(y>=v[mij+1])div2(mij+1,q);
    else div2(p,mij);
}
}
int main()
{
    in>>n;
    for(i=1;i<=n;i++)in>>v[i];
    sort(v+1,v+n+1);
    for(i=1;i<n-1;i++){
        for(j=i+1;j<n;j++){
            y=v[i]+v[j];
            if(v[i]>v[j])x=v[i]-v[j];
            else x=v[j]-v[i];
            p1=div1(j+1,n);
            p2=div2(j+1,n);
            if(p1==p2)if(v[p1]>=x&&v[p1]<=y)nr+=p2-p1+1;
        }
    }

    out<<nr;
    in.close();
    out.close();
    return 0;
}