#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, cnt1 = 0, cnt2 = 0, cnt3 = 0;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    if (i == 0 || i % 3 == 0)
      cnt1 += arr[i];
    else if (i == 1 || i == 4 || i == 7 || i == 10 || i == 13 || i == 16 ||
             i == 19)
      cnt2 += arr[i];
    else
      cnt3 += arr[i];
  }
  if (cnt1 > cnt2 && cnt1 > cnt3)
    cout << "chest";
  else if (cnt2 > cnt1 && cnt2 > cnt3)
    cout << "biceps";
  else
    cout << "back";
  return 0;
}
