#include <bits/stdc++.h>
using ll = long long;
using namespace std;

map<int, vector<int>> g;
map<int, bool> vis;
vector<vector<int>> component;

void dfs(int cur) {
    vis[cur] = true;
    component.back().push_back(cur); // komponens elemeinek eltárolása
    for (int i : g[cur]) {
        if (!vis[i]) {
            dfs(i);
        }
    }
}

int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(0);
    
    int n; cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    for (int i = 0; i < n; i++) g[a[i]].push_back(a[n - 1 - i]);

    vector<int> empty; // ez az empty vektor
    for (int i : a) {
        if (!vis[i]) {
            component.push_back(empty);
            dfs(i);
        }
    }

    vector<pair<int, int>> ans;
    for (auto i : component) {
        sort(i.begin(), i.end());
        bool elso = true;
        for (int j : i) {
            if (elso) { elso = false; continue; }
            ans.push_back({j, i[0]});
        }
    }

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