#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
int n;
cin >> n;
vector<ll> a(n), b(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
}
vector<int> id(n);
iota(begin(id), end(id), 0);
set<ll> p;
do {
ll x = a[id[0]];
ll y = b[id[0]];
bool ok = true;
for (int i = 1; ok && i < n; ++i) {
int j = id[i];
if (x == a[j]) {
y += b[j];
} else if (x == b[j]) {
y += a[j];
} else if (y == a[j]) {
x += b[j];
} else if (y == b[j]) {
x += a[j];
} else {
ok = false;
}
}
if (ok) {
p.insert(min(x, y));
}
} while (next_permutation(begin(id), end(id)));
cout << p.size() << endl;
for (auto& u : p) {
cout << u << "\n";
}
}
