#include <bits/stdc++.h>
using namespace std;
vector<pair<int, int> > rectangles;
set<pair<int, int> > s;
int main() {
int k;
cin >> k;
for (int i = 1; i <= k; i++) {
int a, b;
cin >> a >> b;
rectangles.emplace_back(a, b);
}
for (auto &rect: rectangles) {
s.insert(rect);
}
bool changes = true;
while (changes) {
changes = false;
auto it = s.begin();
auto next_it = next(it);
int a1 = it->first, a2 = it->second;
int b1 = next_it->first, b2 = next_it->second;
if (a1 == b1) {
int new_a1 = a1, new_b1 = a2 + b2;
s.erase(next_it);
s.erase(it);
s.insert({new_a1, new_b1});
changes = true;
} else if (a1 == b2) {
int new_a1 = a1, new_b1 = a2 + b1;
s.erase(next_it);
s.erase(it);
s.insert({new_a1, new_b1});
changes = true;
} else if (a2 == b2) {
int new_a1 = a2, new_b1 = a1 + b1;
s.erase(next_it);
s.erase(it);
s.insert({new_a1, new_b1});
changes = true;
} else if (a2 == b1 && a1 != b2) {
int new_a1 = a2, new_b1 = b2 + a1;
s.erase(next_it);
s.erase(it);
s.insert({new_a1, new_b1});
changes = true;
} else if (a1 == b2 && a2 != b1) {
int new_a1 = a2, new_b1 = b1 + a2;
s.erase(next_it);
s.erase(it);
s.insert({new_a1, new_b1});
changes = true;
} else if (a1 == b2 && b1 == a2) {
int new_a1 = a1, new_b1 = b1 + a2;
int new_a2 = b1, new_b2 = a1 + b2;
s.erase(next_it);
s.erase(it);
s.insert({new_a1, new_b1});
s.insert({new_a2, new_b2});
changes = true;
}
}
cout << s.size() << endl;
for (auto &rect: s) {
cout << min(rect.first, rect.second) << " " << max(rect.first, rect.second) << '\n';
}
return 0;
}
