#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const int MAXN = 200'001;

int a[MAXN], mine;
bool vis[MAXN];
vector<int> c;
vector<int> g[MAXN];
vector<pair<int, int>> ans;

void dfs(int u) {
    vis[u] = true;
    mine = min(mine, u);
    c.emplace_back(u);
    for (int v : g[u]) {
        if (!vis[v]) {
            dfs(v);
        }
    }
}

int main() {
    ios::sync_with_stdio(0); cin.tie(0);
    int n; cin >> n;
    vector<int> comp;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        comp.emplace_back(a[i]);
    }
    sort(comp.begin(), comp.end());
    comp.erase(unique(comp.begin(), comp.end()), comp.end());
    for (int i = 1; i <= n; i++) a[i] = lower_bound(comp.begin(), comp.end(), a[i])-comp.begin();
    for (int i = 1; i <= n; i++) {
        if (a[i] != a[n-i+1]) {
            g[a[i]].emplace_back(a[n-i+1]);
        }
    }

    for (int i = 0; i < comp.size(); i++) {
        if (!vis[i]) {
            mine = 1e9;
            dfs(i);
            for (int j : c) {
                if (j != mine) {
                    ans.emplace_back(comp[j], comp[mine]);
                }
            }
            c.clear();
        }
    }

    cout << ans.size() << "\n";
    for (auto [a, b] : ans) cout << a << " " << b << "\n";
    return 0;
}