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

using ii = pair<int, int>;

int find_bad(const vector<int> &A, int limit = 1e9){
	int res = -1, mx = -1;
	for (int i = 0; i < min(limit, (int)A.size() - 1); i++){
		if (A[i] <= mx) continue;
		if (A[i] > A[i+1]){
			res = i;
		}
		mx = max(mx, A[i]);
	}
	
	return 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_bad(A);
	if (f1 < 0){
		vector<ii> res = {{A[0], A[1]}};
		remove(A, 0); remove(A, 0);
		vector<ii> recur = min_shooting_buildings(A);
		res.insert(res.end(), recur.begin(), recur.end());
		return res;
	}

	int value = A[f1];
	remove(A, f1);
	int f2 = find_bad(A, f1);

	if (f1 > 0 && f2 < 0) f2 = 0;

	if (f2 < 0){
		vector<ii> res = {{value, value}};
		vector<ii> recur = min_shooting_buildings(A);
		res.insert(res.end(), recur.begin(), recur.end());
		return res;
	}

	vector<ii> res = {{value, A[f2]}};
	remove(A, f2);

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