#include <bits/stdc++.h>
using namespace std;
void array_print(int A[], int size) {
  printf("%d", A[0]);
  for (int i = 1; i < size; ++i) {
    printf("%d", A[i]);
  }
  printf("\n");
}
vector<string> vis;
bool isVis(string x) {
  for (int i = 0; i < vis.size(); ++i) {
    if (x == vis[i]) return true;
  }
  return false;
}
int main(int argc, char const *argv[]) {
  int n;
  cin >> n;
  vector<pair<string, string> > v;
  for (int i = 0; i < n; ++i) {
    string a, b;
    cin >> a >> b;
    v.push_back(make_pair(a, b));
  }
  int cnt = 0;
  vector<string> res;
  for (int i = 0; i < v.size(); ++i) {
    string first = v[i].first;
    string last = v[i].second;
    if (isVis(first)) continue;
    bool f = false;
    for (int j = i + 1; j < v.size(); ++j) {
      string temp = v[j].first;
      if (!isVis(temp)) {
        if (temp == last) {
          vis.push_back(last);
          vis.push_back(v[j].first);
          last = v[j].second;
          f = 1;
        }
      }
    }
    if (f) {
      cnt++;
      string tmp = first + " ";
      tmp += last;
      res.push_back(tmp);
    }
    if (!f and !isVis(first) and !isVis(last)) {
      cnt++;
      string tmp = first + " ";
      tmp += last;
      res.push_back(tmp);
    }
  }
  cout << cnt << endl;
  for (int i = 0; i < res.size(); ++i) {
    cout << res[i] << endl;
  }
  return 0;
}
