G

#include <array>
#include <iostream>
#include <vector>
#include <map>

using namespace std;

#define int long long

const long long INF = 1e18 + 7;
const int MAXN = 2e5 + 10;
const int N = 2e5;

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n;
    cin >> n;
    map<string, string> start, tmp;
    for (int i = 0; i < n; ++i) {
        string old, nw;
        cin >> old >> nw;
        if (!tmp.contains(old)) {
            start[old] = nw;
            tmp[nw] = old;
        } else {
            string cur = tmp[old];
            start[cur] = nw;
            tmp[nw] = cur;
        }
    }
    cout << start.size() << '\n';
    for (auto& [x, y]: start) {
        cout << x << ' ' << y << '\n';
    }
}