#include<fstream>
#include<algorithm>
using namespace std;
ifstream cin("nrtri.in");
ofstream cout("nrtri.out");
int a[800],b[30001];
int main()
{
    int j=0,k=0,n;
    cin>>n;
    for(int i=0;i<n;cin>>a[i++]);
    sort(a,a+n);
    for(int i=a[0]+1;i<=a[n-1]-a[1];b[i++]=j)
        for(;a[j]<i;++j);
    for(int i=1;i<n-1;++i)
        for(int j=i+1;j<n&&a[j]<=2*a[i];k+=i-b[a[j++]-a[i]]);
    return cout<<k,0;
}