#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline T S(T a) {
  return a * a;
}
template <class T>
inline string tostring(T a) {
  ostringstream os("");
  os << a;
  return os.str();
}
template <typename T>
inline long long tolong(T a) {
  long long res;
  istringstream os(a);
  os >> res;
  return res;
}
template <typename T>
inline T gcd(T a, T b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
template <typename T>
inline T bigmod(T a, T b, T m) {
  if (b == 0)
    return 1;
  else if (b % 2 == 0)
    return S(bigmod(a, b / 2, m)) % m;
  else
    return (a % m * bigmod(a, b - 1, m)) % m;
}
const int inf = (int)1e9 + 5;
const long long linf = (long long)1e16 + 5;
const long long modd = (long long)1e9 + 7;
const int mod = 10000007;
void pr(int f) {
  if (f == 1)
    cout << "YES\n";
  else
    cout << "NO\n";
}
int vt[11111111];
int z, s;
map<string, string> mapp;
string a, b;
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  int cnt = n;
  while (n--) {
    cin >> a >> b;
    if (mapp.find(a) == mapp.end())
      mapp[b] = a;
    else {
      string t = mapp[a];
      mapp.erase(a);
      mapp[b] = t;
      cnt--;
    }
  }
  cout << cnt << endl;
  map<string, string>::iterator i;
  for (auto i = mapp.begin(); i != mapp.end(); ++i)
    cout << i->second << " " << i->first << endl;
}
