#include <iostream>
#include <iomanip>
#include <sstream>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <functional>
#include <iterator>
#include <limits>
#include <numeric>
#include <utility>
#include <type_traits>
#include <cmath>
#include <cassert>
#include <cstdio>

using namespace std;
using namespace placeholders;

using LL = long long;
using ULL = unsigned long long;
using VI = vector< int >;
using VVI = vector< vector< int > >;
using VS = vector< string >;
using ISS = istringstream;
using OSS = ostringstream;
using PII = pair< int, int >;
using VPII = vector< pair< int, int > >;
template < typename T = int > using VT = vector< T >;
template < typename T = int > using VVT = vector< vector< T > >;
template < typename T = int > using LIM = numeric_limits< T >;

template < typename T > inline istream& operator>>( istream &s, vector< T > &v ){ for ( T &t : v ) { s >> t; } return s; }
template < typename T > inline ostream& operator<<( ostream &s, const vector< T > &v ){ for ( int i = 0; i < int( v.size() ); ++i ){ s << ( " " + !i ) << v[i]; } return s; }

void in_impl(){};
template < typename T, typename... TS > void in_impl( T &head, TS &... tail ){ cin >> head; in_impl( tail ... ); }
#define IN( T, ... ) T __VA_ARGS__; in_impl( __VA_ARGS__ );

template < typename T > struct getv_fmt;
template <> struct getv_fmt<       int >{ static constexpr const char *fmt = "%d"; };
template <> struct getv_fmt< long long >{ static constexpr const char *fmt = "%lld"; };
template < typename T > void getv( std::vector< T > &v ){ for_each( begin( v ), end( v ), []( T &a ){ scanf( getv_fmt< T >::fmt, &a ); } ); };

template < typename T > inline T fromString( const string &s ) { T res; istringstream iss( s ); iss >> res; return res; }
template < typename T > inline string toString( const T &a ) { ostringstream oss; oss << a; return oss.str(); }

#define NUMBERED( name, number ) NUMBERED2( name, number )
#define NUMBERED2( name, number ) name ## _ ## number
#define REP1( n ) REP2( NUMBERED( REP_COUNTER, __LINE__ ), n )
#define REP2( i, n ) REP3( i, 0, n )
#define REP3( i, m, n ) for ( int i = ( int )( m ); i < ( int )( n ); ++i )
#define GET_REP( a, b, c, F, ... ) F
#define REP( ... ) GET_REP( __VA_ARGS__, REP3, REP2, REP1 )( __VA_ARGS__ )
#define FOR( e, c ) for ( auto &&e : c )
#define ALL( c ) begin( c ), end( c )
#define AALL( a ) ( remove_all_extents< decltype( a ) >::type * )a, ( remove_all_extents< decltype( a ) >::type * )a + sizeof( a ) / sizeof( remove_all_extents< decltype( a ) >::type )
#define DRANGE( c, p ) begin( c ), begin( c ) + ( p ), end( c )

#define SZ( v ) ( (int)( v ).size() )
#define EXIST( c, e ) ( ( c ).find( e ) != ( c ).end() )

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

#define PB push_back
#define EM emplace
#define EB emplace_back
#define BI back_inserter

#define MP make_pair
#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

constexpr int INF = LIM<>::max() / 2;

// セグメント木のユーティリティ
inline int chl( const int k )
{
	return k * 2 + 1;
}

inline int chr( const int k )
{
	return k * 2 + 2;
}

inline int mid( const int l, const int r )
{
	return ( l + r ) / 2;
}

#define LEFT( k, l, r ) chl( k ), l, mid( l, r )
#define RIGHT( k, l, r ) chr( k ), mid( l, r ), r

// セグメント木による Range (Minimum|Maximum) Query
template < typename T = int, typename F = std::less< T >,
		 T identity = std::is_same< F, std::less< T > >::value ? std::numeric_limits< T >::max() : std::numeric_limits< T >::min(),
		 typename = typename std::enable_if< std::is_same< F, std::less< T > >::value || std::is_same< F, std::greater< T > >::value >::type >
class RangeMQuery
{
private:
	const int N;
	std::vector< T > data;

	F func;

public:
	RangeMQuery( const int n ) :
		N( n ), data( N * 4, identity )
	{
		return;
	}
	
	RangeMQuery( const std::vector< T > &src ) :
		N( src.size() ), data( N * 4 )
	{
		init( src, 0, 0, N );
		return;
	}

	void update( const int p, const T x )
	{
		return update( p, x, 0, 0, N );
	}

	T query( const int a, const int b ) const
	{
		return query( a, b, 0, 0, N );
	}

private:
	void init( const vector< T > &src, const int k, const int l, const int r )
	{
		if ( l + 1 == r )
		{
			data[k] = src[l];
			return;
		}

		init( src, LEFT( k, l, r ) );
		init( src, RIGHT( k, l, r ) );
		data[k] = std::min( data[ chl( k ) ], data[ chr( k ) ], func );

		return;
	}

	void update( const int p, const T x, const int k, const int l, const int r )
	{
		if ( p < l || r <= p )
		{
			return;
		}
		if ( l + 1 == r && p == l )
		{
			data[k] = x;
			return;
		}

		update( p, x, chl( k ), l, mid( l, r ) );
		update( p, x, chr( k ), mid( l, r ), r );
		data[k] = std::min( data[ chl( k ) ], data[ chr( k ) ], func );
	
		return;
	}

	T query( const int a, const int b, const int k, const int l, const int r ) const
	{
		if ( b <= l || r <= a )
		{
			return identity;
		}
		else if ( a <= l && r <= b )
		{
			return data[k];
		}
		else
		{
			return std::min( query( a, b, chl( k ), l, mid( l, r ) ), query( a, b, chr( k ), mid( l, r ), r ), func );
		}
	}
};
// RangeMQuery< comp = less, identity element = inf >( N )
// RangeMQuery< comp = less, identity element = inf >( VT src )
// update( pos, x )
// query( [ a, b ) )

VI poss;

map< PII, VPII > nexts;

PII solve( const int L, const int R, RangeMQuery<> &rmq1, RangeMQuery<> &rmq2 )
{
	if ( R <= L )
	{
		return { INF, INF };
	}

	const int a = rmq1.query( L, R );
	const int p = poss[a];
	const int b = rmq2.query( p + 1, R );
	const int q = poss[b];

	VPII &next = nexts[ MP( a, b ) ];
	next.PB( solve( L, p, rmq1, rmq2 ) );
	next.PB( solve( p + 1, q, rmq2, rmq1 ) );
	next.PB( solve( q + 1, R, rmq1, rmq2 ) );

	return { a, b };
}

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );
	cout << setprecision( 12 ) << fixed;

	int N;
	scanf( "%d", &N );

	VI A( N );
	getv( A );

	poss.resize( N + 1 );
	RangeMQuery<> rmq_e( N ), rmq_o( N );
	REP( i, N )
	{
		poss[ A[i] ] = i;
		( i % 2 ? rmq_o : rmq_e ).update( i, A[i] );
	}

	priority_queue< PII, VPII, greater< PII > > que;
	que.push( solve( 0, N, rmq_e, rmq_o ) );
	REP( i, N / 2 )
	{
		const PII p = que.top();
		que.pop();

		cout << p.fst << ' ' << p.snd << ( i + 1 == N / 2 ? '\n' : ' ' );

		FOR( pp, nexts[p] )
		{
			que.push( pp );
		}
	}
	cout << flush;

	return 0;
}


Measured memory_bytes: 42360