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

struct dsu
{
int n;
vector<int> id;
//vector<int> s;
void build(int size)
	{
	n=size;
	id.resize(n+1);
	//s.resize(n+1,1);
	iota(id.begin(),id.end(),0);
	}
int find(int a)
	{
	if(id[a]==a)return a;
	else return id[a]=find(id[a]);
	}
void unio(int a,int b)
	{
	a=find(a);
	b=find(b);
	id[a]=b;
	}
};

int main() {
	dsu k;
	
	int n;
	cin>>n;
	vector<pair<int,int>> a(n);
	vector<int> idtoval(n);
	map<int,int> vis;
	int cnt=1;
	for(int i=0;i<n;i++)
		{
		cin>>a[i].first;
		if(vis[a[i].first]){a[i].second=vis[a[i].first];}
		else
			{
			idtoval[cnt]=a[i].first;
			a[i].second=cnt;
			vis[a[i].first]=cnt++;
			}
		}
	k.build(cnt);
	vector<pair<int,int>> ans;
	for(int l=0,r=n-1;l<r;l++,r--)
		{
		if(k.find(a[l].second)!=k.find(a[r].second))
			{
			int x=idtoval[k.find(a[r].second)];
			int y=idtoval[k.find(a[l].second)];
			if(y<x)
				{
				
				k.unio(a[r].second, a[l].second);
				ans.push_back({x,y});
				}
			else
				{
				k.unio(a[l].second, a[r].second);
				ans.push_back({y,x});
				}
			}
		}
	cout<<ans.size()<<"\n";
	for(auto [x,y]:ans)cout<<x<<" "<<y<<"\n";
}