// UUID: 68f8444e-ccb9-49b2-bc6f-66e4ce1d532c
#include <bits/stdc++.h>
 
using namespace std;
 
#define ll long long
#define fs first
#define sc second
#define pb push_back
#define pll pair<ll, ll>
#define vll vector<ll>
#define v2ll vector<vll>

const ll MOD = 1e9+7;
const ll INF = LONG_LONG_MAX;

ll n;
vll v;
map<ll, set<ll>> g;
map<ll, bool> vis;
set<ll> s;
vector<set<ll>> anss;

void dfs(ll p) {
    vis[p] = true;
    s.insert(p);
    for (ll i : g[p]) {
        if (!vis[i]) {
            dfs(i);
        }
    }
}

void solve()
{
    cin >> n;
    v.resize(n);
    for (ll &i : v) cin >> i;
    for (ll i = 0; i < n; i++) {
        g[v[i]].insert(v[n-i-1]);
        g[v[n-i-1]].insert(v[i]);
    }
    ll ans = 0;
    for (ll i : v) {
        if (!vis[i]) {
            dfs(i);
            ans += s.size()-1;
            anss.push_back(s);
            s.clear();
        }
    }
    cout << ans << '\n';
    for (auto i : anss) {
        for (auto j : i) {
            if (j == *i.begin()) continue;
            cout << j << ' ' << *i.begin() << '\n';
        }
    }
}
 
main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    ll t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}