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

template<typename T>bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<typename T>bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}


// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts) {
   return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

// std::vector Initialization
template<typename T>
void fill_all(T& arr, const T& v) { arr = v; }
template<typename T, typename U>
void fill_all(T& arr, const U& v) { for (auto& i : arr) fill_all(i, v); }

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
   os << "[";
   bool a = 1;
   for (auto e : v ) {
      os << (a ? "" : " "); 
      os << e;
      a = 0;
   }
   os << "]";
   return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
   os << "(" << p.first << " " << p.second << ")";
   return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
   os << "{";
   bool a = 1;
   for (auto e : st) {
      os << (a ? "" : " ");
      os << e;
      a = 0;
   }
   os << "}";
   return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
   os << "{";
   bool a = 1;
   for (auto e : mp) {
      os << (a ? "" : " ");
      os << e.first << ":" << e.second;
      a = 0;
   }
   os << "}";
   return os;
}

// std::tuple Debug
template<int N,class Tuple>
void out(ostream &os,const Tuple &t){}
template<int N,class Tuple,class H,class ...Ts>
void out(ostream &os,const Tuple &t){
   if(N)os<<" ";
   os<<get<N>(t);
   out<N+1,Tuple,Ts...>(os,t);
}
template<class ...Ts>
ostream& operator<<(ostream &os, const tuple<Ts...> &t){
   os<<"(";
   out<0,tuple<Ts...>,Ts...>(os,t);
   os<<")";
   return os;
}

// Debug
#define DUMP(x) cout<<#x<<" = "<<(x)<<endl

struct edge { int to, cost; };

const LL LINF = 1LL<<60;
const int IINF = 1<<30;
const LL MOD = 1e9+7;

template<typename Monoid>
struct SegmentTree {

   using F = function<Monoid(Monoid,Monoid)>;

   int sz;
   vector< Monoid > data;
   const F f;
   const Monoid M1;

   SegmentTree(int n, const F f, const Monoid &M1) : f(f), M1(M1) {
      sz = 1;
      while(sz < n) sz <<= 1;
      data.assign(2 * sz, M1);
   }

   void set(int k, const Monoid &x) {
      data[k + sz] = x;
   }

   void build() {
      for(int k = sz - 1; k > 0; --k) {
         data[k] = f(data[2 * k + 0], data[2 * k + 1]);
      }
   }

   Monoid query(int a, int b, int k, int l, int r) {
      if (r <= a || b <= l) {
         return M1;
      } else if (a <= l && r <= b) {
         return data[k];
      } else {
         return f(query(a, b, 2 * k + 0, l, (l + r) / 2),
               query(a, b, 2 * k + 1, (l + r) / 2, r));
      }
   }

   Monoid query(int a, int b) {
      // return f[a, b).
      return query(a, b, 1, 0, sz);
   }
};

template<typename T, typename U, typename V>
struct trio {
   T first;
   U second;
   V third;

   bool operator<(const trio<T,U,V>& rhs) const {
      pair<T,pair<U,V>> l{first,{second,third}},
         r{rhs.first,{rhs.second,rhs.third}};
      return l < r;
   }

   bool operator>(const trio<T,U,V>& rhs) const {
      return rhs < *this;
   }
};

// trio Debug
template<typename T, typename U, typename V>
ostream& operator<<(ostream& os, const trio<T, U, V>& t) {
   os << "(" << t.first << " " << t.second << " " << t.third << ")";
   return os;
}

int main()
{
   int N; cin >> N;
   vector<int> p(N);
   for (int i = 0; i < N; ++i) {
      cin >> p[i];
   }

   SegmentTree<pair<int,int>> even(N,
         [](pair<int,int> a, pair<int,int> b){ return min(a, b); }, {IINF,-1});
   SegmentTree<pair<int,int>> odd(N,
         [](pair<int,int> a, pair<int,int> b){ return min(a, b); }, {IINF,-1});

   for (int i = 0; i < N; ++i) {
      if (i % 2 == 0) {
         even.set(i, {p[i],i});
         odd.set(i, {IINF,-1});
      } else {
         odd.set(i, {p[i],i});
         even.set(i, {IINF,-1});
      }
   }

   even.build();
   odd.build();

   priority_queue<trio<int,int,int>, vector<trio<int,int,int>>, greater<trio<int,int,int>>> que;
   que.push({ even.query(0, N).first, 0, N });

   vector<int> ans;

   for (int k = 0; k < N/2; ++k) {

      int l = que.top().second, r = que.top().third;
      que.pop();

      int i, j;
      if (l % 2 == 0) {
         i = even.query(l, r).second;
         j = odd.query(i+1, r).second;
      } else {
         i = odd.query(l, r).second;
         j = even.query(i+1, r).second;
      }

      ans.push_back(p[i]);
      ans.push_back(p[j]);

      if (l < i) que.push({l % 2 == 0 ? even.query(l, i).first : odd.query(l, i).first, l, i});
      if (i+1 < j) que.push({(i+1) % 2 == 0 ? even.query(i+1, j).first : odd.query(i+1, j).first, i+1, j});
      if (j+1 < r) que.push({(j+1) % 2 == 0 ? even.query(j+1, r).first : odd.query(j+1, r).first, j+1, r});
   }

   for (int i = 0; i < N; ++i) {
      cout << ans[i] << (i == N-1 ? "\n" : " ");
   }

   return 0;
}


Measured memory_bytes: 11944