#include <bits/stdc++.h>
using namespace std;
template <typename T>
T expo(T e, T n) {
  T x = 1, p = e;
  while (n) {
    if (n & 1) x = x * p;
    p = p * p;
    n >>= 1;
  }
  return x;
}
template <typename T>
T power(T e, T n, T m) {
  T x = 1, p = e;
  while (n) {
    if (n & 1) x = (x * p) % m;
    p = (p * p) % m;
    n >>= 1;
  }
  return x;
}
template <typename T>
T InverseEuler(T a, T m) {
  return (a == 1 ? 1 : power(a, m - 2, m));
}
template <typename T>
T gcd(T a, T b) {
  while (a %= b ^= a ^= b ^= a)
    ;
  return b;
}
template <typename T>
T lcm(T a, T b) {
  return (a * (b / gcd(a, b)));
}
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
map<string, long long> M;
map<long long, string> invM;
long long n = 1;
vector<long long> g[5000], temp;
bool vis[5000];
long long in[5000], out[5000];
vector<pair<string, string> > ans;
void dfs(long long node) {
  vis[node] = true;
  temp.push_back(node);
  for (auto it : g[node]) {
    if (!vis[it]) {
      dfs(it);
    }
  }
  return;
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long q;
  cin >> q;
  for (__typeof(q) i = 1; i <= q; ++i) {
    string s, second;
    cin >> s >> second;
    if (M.find(s) == M.end()) {
      M[s] = n;
      invM[n] = s;
      n++;
    }
    if (M.find(second) == M.end()) {
      M[second] = n;
      invM[n] = second;
      n++;
    }
    g[M[s]].push_back(M[second]);
    in[M[second]] += 1;
    out[M[s]] += 1;
  }
  long long components = 0;
  for (__typeof(n - 1) i = 1; i <= n - 1; ++i) {
    if (!vis[i]) {
      components++;
      temp.clear();
      dfs(i);
      string A, B;
      for (auto it : temp) {
        if (in[it] == 0) A = invM[it];
        if (out[it] == 0) B = invM[it];
      }
      ans.push_back({A, B});
    }
  }
  cout << components << '\n';
  for (auto it : ans) {
    cout << it.first << " " << it.second << '\n';
  }
  return 0;
}
