#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
const int N = 1e5;
const int MX = 2e5 + 5;
const int64_t mod = 1000000007;
const int64_t PI = acos((int64_t)-1);
static string x, y;
unordered_map<string, string> par;
vector<pair<string, string>> vs, ans;
set<string> st;
void makeset(string n) { par[n] = n; }
string Find(string boss) {
  if (par[boss] == boss) return boss;
  return par[boss] = Find(par[boss]);
}
void Union(string a, string b) {
  string u = Find(a);
  string v = Find(b);
  if (u != v) par[u] = v;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int64_t t, i = 1;
  cin >> t;
  while (t--) {
    cin >> x >> y;
    vs.push_back({x, y});
    st.insert(x);
    st.insert(y);
  }
  for (auto x : st) makeset(x);
  for (auto x : vs) Union(x.first, x.second);
  for (auto x : vs) {
    y = Find(x.first);
    if (st.find(y) != st.end()) {
      ans.push_back({x.first, y});
      st.erase(y);
    }
  }
  cout << ans.size() << "\n";
  for (auto x : ans) cout << x.first << " " << x.second << "\n";
  return (0);
}
