#include <bits/stdc++.h>
using namespace std;
const int c=2e5+5;

int n;
int arr[c];
vector<int> adj[c];
vector<int> comp;
bool vis[c];
vector<pair<int,int>> ans;

void dfs(int v, int val){
    vis[v]=1;
    for(int x:adj[v]){
        if(!vis[x]){
            ans.push_back(make_pair(comp[x], val));
            dfs(x, val);
        }
    }
}

int f(int k){
    return lower_bound(comp.begin(),comp.end(),k)-comp.begin();
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    cin>>n;

    comp.push_back(0);
    for(int i=1;i<=n;i++){
        cin>>arr[i];
        comp.push_back(arr[i]);
    }

    sort(comp.begin(), comp.end());
    comp.resize(unique(comp.begin(),comp.end())-comp.begin());

    for(int i=1;i<=n;i++){
        int a = n-i+1;
        if(arr[i]==arr[a]) continue;
        adj[f(arr[i])].push_back(f(arr[a]));
    }

    for(int i=1;i<comp.size();i++){
        if(!vis[i]) dfs(i,comp[i]);
    }

    cout << ans.size() << '\n';
    for(pair<int,int> x:ans){
        cout << x.first << ' ' << x.second << '\n';
    }
}