#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cout.precision(15);
  cout << fixed;
  cout.tie(0);
  int test;
  int n, chest, biceps, backs;
  vector<int> vi, vii;
  cin >> n;
  int val;
  chest = biceps = backs = 0;
  for (int i = 1; i <= n; ++i) {
    cin >> val;
    if (i == 1 || i == 4 || i == 7 || i == 10 || i == 13 || i == 16 || i == 19)
      chest += val;
    else if (i == 2 || i == 5 || i == 8 || i == 11 || i == 14 || i == 17 ||
             i == 20)
      biceps += val;
    else
      backs += val;
  }
  if (chest > biceps && chest > backs)
    cout << "chest" << endl;
  else if (biceps > chest && biceps > backs)
    cout << "biceps" << endl;
  else
    cout << "back" << endl;
  vi.clear();
  vii.clear();
  return 0;
}
