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#include <bits/stdc++.h>

using namespace std;

#define IOF ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
#define ll long long
#define ull unsigned long long

#define fi first
#define se second
#define all(v) v.begin(), v.end()
#define allR(v) v.rbegin(), v.rend()
#define sz(x) (int)x.size()

const double eps = 1e-9;
const int N = 1e5 + 5;
const int M = 1e9 + 7;

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

typedef __gnu_pbds::tree<int, __gnu_pbds::null_type, less<>, __gnu_pbds::rb_tree_tag, __gnu_pbds::tree_order_statistics_node_update> ordered_set;

void FIO() {
#ifndef ONLINE_JUDGE
    freopen("../in.txt", "r", stdin);
    freopen("../out.txt", "w", stdout);
#endif
}

int dx[]{0, 1, 0, -1, 1, 1, -1, -1};
int dy[]{1, 0, -1, 0, 1, -1, -1, 1};
char di[]{'R', 'D', 'L', 'U'};

void multiVerse() {
    int n;
    cin >> n;
    map<string, string> mp;
    for (int i = 0; i < n; ++i) {
        string s, t;
        cin >> s >> t;

        for (auto &j: mp) {
            if (s == j.se) {
                s = j.fi;
                break;
            }
        }

        mp[s] = t;
    }
    cout << sz(mp) << '\n';
    for (auto &i: mp) {
        cout << i.fi << " " << i.se << '\n';
    }
}

int main() {
    IOF
    FIO();
    int tt = 1;
//    cin >> tt;

    while (tt--) {
        multiVerse();
    }

    return 0;
}