#include <bits/stdc++.h>
using namespace std;
void start_func() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
long long spf[100010];
string olds[100010], news[100010];
map<string, string> parent;
map<string, long long> mk;
vector<pair<string, string>> v;
string find(string x) {
  mk[x] = 1;
  if (parent[x].size() == 0) {
    return x;
  }
  return parent[x] = find(parent[x]);
}
void solve() {
  long long n;
  cin >> n;
  for (long long i = 1; i <= n; i++) {
    cin >> olds[i] >> news[i];
    parent[olds[i]] = news[i];
  }
  for (long long i = 1; i <= n; i++) {
    if (mk[olds[i]] == 0) {
      string temp = find(olds[i]);
      v.push_back({olds[i], temp});
    }
  }
  cout << v.size() << '\n';
  for (auto i : v) {
    cout << i.first << " " << i.second << "\n";
  }
}
signed main() {
  start_func();
  long long t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
