#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

//#define FILE 10
#define int int64_t

using namespace std;
using namespace __gnu_pbds;

template<typename T>
using orset = tree <T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename K>
using ormap = tree <T, K, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
mt19937_64 rnd(chrono::steady_clock::now().time_since_epoch().count());

const int N = 1e5;

int sqr(int x)
{
    return x * x;
}

void solve()
{
    int n;
    cin >> n;
    vector <pair <string, string>> ans;
    map <char, string> now;
    while (n--)
    {
        string s;
        cin >> s;
        if (now [s.back()] != "")
        {
            ans.push_back({now [s.back()], s});
            now.erase(s.back());
        }
        else
            now [s.back()] = s;
    }
    cout << ans.size() << "\n";
    for (auto i: ans)
        cout << i.first << " " << i.second << "\n";
}

int32_t main(int32_t argc, char* argv[]) {
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    #ifdef FILE
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif
    int t = 1;
    //cin >> t;
    while (t--)
        solve();
}