#include <bits/stdc++.h>
using namespace std;

using ii = pair<int, int>;

int find_best(const vector<int> &A, int limit = -1, int value = 0){
	int bad_res = -1, good_res = -1, mx = 0;
	for (int i = 0; i < (int)A.size(); i++){
		if (i >= limit) mx = max(mx, value);
		if (A[i] <= mx) continue;
		if (i < (int)A.size() - 1 && A[i] > A[i+1]){
			if (bad_res < 0) bad_res = i;
		}
		else if (good_res < 0) good_res = i;
		mx = max(mx, A[i]);
	}

	if (bad_res >= 0) return bad_res;
	return good_res;
}

void remove(vector<int> &A, int idx){
	vector<int> newA;
	for (int i = 0; i < (int)A.size(); i++){
		if (i != idx) newA.push_back(A[i]);
	}
	swap(A, newA);
}

vector<ii> min_shooting_buildings(vector<int> A){
	if ((int)A.size() == 0) return {};
	if ((int)A.size() == 1) return {{A[0], A[0]}};

	int f1 = find_best(A);
	int value = A[f1];
	remove(A, f1);

	int f2 = find_best(A, f1, value);
	int val2 = (f2 < 0) ? value : A[f2];
	if (f2 >= 0) remove(A, f2);

	vector<ii> res = {{value, val2}};
	vector<ii> recur = min_shooting_buildings(A);
	res.insert(res.end(), recur.begin(), recur.end());

	return res;
}