#include <bits/stdc++.h>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int main()
{
    int n,i,st,dr,cnt=0;
    fin>>n;
    int v[n+1];
    for(i=1;i<=n;++i){
        fin>>v[i];
    }
    for(i=3;i<=n;++i){
        st=1;
        dr=i-1;
        while(st<dr){
            if(v[st]+v[dr]>v[i]){
                cnt++;
                if(v[st+1]+v[dr]>v[i]){
                    st++;
                }
                else{
                    dr--;
                }
            }
            else{
                st++;
            }
        }
    }
    fout<<cnt;
    return 0;
}