#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const long long INF = 0x3f3f3f3f3f3f3f3f;
inline long long read() {
  long long first = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    first = first * 10 + ch - '0';
    ch = getchar();
  }
  return first * f;
}
inline void ou(long long first) {
  char ch[25];
  int len = 0;
  if (first < 0) {
    putchar('-');
    first = ~first + 1;
  }
  do {
    ch[len++] = first % 10 + '0';
    first /= 10;
  } while (first > 0);
  for (int i = len - 1; i >= 0; i--) putchar(ch[i]);
  return;
}
const int maxn = 3e4 + 5;
const int N = 210;
int main() {
  int t = read();
  int cnt = 1;
  map<string, int> mp1;
  map<int, string> mp2;
  string ans[maxn];
  while (t--) {
    string a, b;
    cin >> a >> b;
    if (mp1[a] == 0) {
      ans[cnt] = a;
      mp1[a] = cnt;
      mp1[b] = cnt;
      mp2[cnt++] = b;
    } else {
      mp2[mp1[a]] = b;
      mp1[b] = mp1[a];
    }
  }
  ou(cnt - 1), puts("");
  for (int i = 1; i <= cnt - 1; i++) {
    cout << ans[i] << ' ';
    cout << mp2[mp1[ans[i]]] << '\n';
  }
  return 0;
}
