#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,i,j,cnt,v[801];

int cautbin(int st,int dr,int x) {
    while (st<=dr) {
        int mid=(st+dr)/2;
        if (v[mid]<=x)
            st=mid+1;
        else
            dr=mid-1;
    }
    return dr;
}

int main() {
    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];
    sort(v+1,v+n+1);
    for (i=1;i<n-1;i++)
        for (j=i+1;j<n;j++)
            cnt+=cautbin(j+1,n,v[i]+v[j])-j;
    fout<<cnt;
    return 0;
}