#include <bits/stdc++.h>
using namespace std;
int main() {
  int number, chest = 0, biceps = 0, backs = 0, user_input;
  cin >> number;
  for (int x = 1; x <= number; x += 1) {
    cin >> user_input;
    if (x % 3 == 1) {
      chest += user_input;
    } else if (x % 3 == 2) {
      biceps += user_input;
    } else if (x % 3 == 0) {
      backs += user_input;
    }
  }
  int highest = max(chest, max(biceps, backs));
  if (highest == chest) {
    cout << "chest";
  } else if (highest == biceps) {
    cout << "biceps";
  } else if (highest == backs) {
    cout << "back";
  }
  return 0;
}
