#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define REP(i,n) for(long long i = 0; i < (n); i++)
#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQR = priority_queue<T,vector<T>,greater<T>>;

constexpr long long MOD = (long long)1e9 + 7;
constexpr long long MOD2 = 998244353;
constexpr long long HIGHINF = (long long)1e18;
constexpr long long LOWINF = (long long)1e15;
constexpr long double PI = 3.1415926535897932384626433;

template <class T> vector<T> make_v(size_t N,T init){return vector<T>(N,init);}
template <class... T> auto make_v(size_t N,T... t){return vector<decltype(make_v(t...))>(N,make_v(t...));}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) {o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o;}
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const multiset<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) {o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o;}
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) {o << "{" << obj.first << ", " << obj.second << "}"; return o;}
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
void print(void) {cout << endl;}
template <class Head> void print(Head&& head) {cout << head;print();}
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) {cout << head << " ";print(forward<Tail>(tail)...);}
template <class T> void chmax(T& a, const T b){a=max(a,b);}
template <class T> void chmin(T& a, const T b){a=min(a,b);}
void YN(bool flg) {cout << (flg ? "YES" : "NO") << endl;}
void Yn(bool flg) {cout << (flg ? "Yes" : "No") << endl;}
void yn(bool flg) {cout << (flg ? "yes" : "no") << endl;}

template<class T> class Segment_Tree_Range_Minimum_Query {
	size_t N,M;
	T ini;
	vector<T> node;

public:
	Segment_Tree_Range_Minimum_Query(const vector<T> & ar, const T ini) : M(ar.size()), ini(ini) {
		for (N = 1; N < M; N *= 2);
		node.resize(2 * N - 1, ini);
		for (int i = 0; i<M; ++i) node[i + N - 1] = ar[i];
		for (int i = N - 2; i >= 0; --i) node[i] = min(node[2 * i + 1], node[2 * i + 2]);
	}

	Segment_Tree_Range_Minimum_Query(const size_t M, const T ini) : M(M), ini(ini) {
		for (N = 1; N < M; N *= 2);
		node.resize(2 * N - 1, ini);
	}

	void update(size_t idx, const T var) {
		idx += (N - 1);
		node[idx] = var;
		while (idx > 0) {
			idx = (idx - 1) / 2;
			node[idx] = min(node[2 * idx + 1], node[2 * idx + 2]);
		}
	}

	T getvar(const int a, const int b, int k = 0, int l = 0, int r = -1) {
		if (r < 0) r = N;
		if (r <= a || b <= l) return ini;
		if (a <= l && r <= b) return node[k];
		T vl = getvar(a, b, 2 * k + 1, l, (l + r) / 2);
		T vr = getvar(a, b, 2 * k + 2, (l + r) / 2, r);
		return min(vl, vr);
	}

	T operator[](size_t idx) {
		return node[idx + N - 1];
	}

	T operator[](pair<size_t, size_t> p) {
		return getvar(p.first, p.second);
	}
	
	void print() {
		cout << "{ " << getvar(0, 1);
		for (int i = 1; i < M; ++i) cout << ", " << getvar(i, i + 1);
		cout << " }" << endl;
	}
};

const int MAX_N = 200010;
int N;    
vector<int> A(MAX_N);
vector<vector<int>> edge(MAX_N);
vector<int> match(MAX_N,-1);

Segment_Tree_Range_Minimum_Query<pair<int,int>> SegL(MAX_N,{MAX_N,MAX_N}),SegR(MAX_N,{MAX_N,MAX_N});

pair<int,int> rec(int l, int r) {
    
    auto e1 = (l%2?SegR:SegL).getvar(l,r+1);
    int s = e1.second;
    auto e2 = (l%2?SegL:SegR).getvar(s,r+1);
    int t = e2.second;
    match[s] = t;

    if(0<=l&&l<=s-1&&s-1<=r&&r<N){
        pair<int,int> vl = rec(l,s-1);
        edge[s].push_back(vl.first);
    }
    if(0<=l&&l<=s+1&&s+1<t-1&&t-1<=r&&r<N) {
        pair<int,int> vc = rec(s+1,t-1);
        edge[s].push_back(vc.first);
    }
    if(0<=l&&l<=t+1&&t+1<r&&r<N){
        pair<int,int> vr = rec(t+1,r);
        edge[s].push_back(vr.first);
    }
    pair<int,int> ret = {s,t};
    return ret;
}

int main() {
    cin >> N;
    for(int i = 0; i < N; ++i) cin >> A[i];
    for(int i = 0; i < N; ++i) (i%2?SegR:SegL).update(i,{A[i],i});
    auto p = rec(0,N-1);
    PQR<pair<int,int>> pq;
    pq.push({A[p.first],p.first});
    vector<int> ans;
    while(pq.size()) {
        auto from = pq.top().second;
        pq.pop();
        ans.push_back(A[from]);
        ans.push_back(A[match[from]]);
        for (auto to:edge[from]) pq.push({A[to],to});
    }
    for(auto e:ans) cout << e << " ";
    cout << endl;

 
	return 0;
}


Measured memory_bytes: 40308