#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int q;
  cin >> q;
  unordered_map<string, string> gr;
  set<string> ending;
  for (int i = 0; i < q; i++) {
    string prev, next;
    cin >> prev >> next;
    gr[prev] = next;
    ending.insert(next);
  }
  vector<pair<string, string>> ans;
  for (auto it : gr) {
    if (ending.count(it.first)) continue;
    string cur = it.first;
    while (gr.count(cur)) {
      cur = gr[cur];
    }
    ans.push_back({it.first, cur});
  }
  cout << ans.size() << "\n";
  for (auto it : ans) cout << it.first << " " << it.second << "\n";
  return 0;
}
