#include <bits/stdc++.h>

using namespace std;

const int Z = (int)1e5 + 111;
const int INF = (int)1e9;

int l[Z], r[Z], b[Z], dp[Z];

int main() {
  int m;
  cin >> m;
  l[Z - 1] = INF;
  for (int i = 0; i <= m + 1; ++i)
    b[i] = Z - 1;
  for (int i = 1;; ++i) {
    cin >> l[i] >> r[i];
    if (l[i] == 0 && r[i] == 0)
      break;
    if (l[i] == r[i] || r[i] <= 0 || l[i] >= m) continue;
    if (l[b[min(m, r[i])]] > l[i])
      b[min(m, r[i])] = i;
  }
  for (int i = m; i; --i) {
    if (l[b[i + 1]] < l[b[i]])
      b[i] = b[i + 1];
    if (i && i == l[b[i]] || b[i] == Z - 1) {
      cout << "No solution";
      exit(0);
    }
  }
  vector<int> v;
  for (int i = m; i;) {
    v.push_back(b[i]);
    i = max(0, l[b[i]]);
  }
  cout << v.size() << "\n";
  vector<pair<int, int>> ans;
  for (auto &x : v)
    ans.push_back({l[x], r[x]});
  sort(ans.begin(), ans.end());
  for (auto &x : ans)
    cout << x.first << " " << x.second << "\n";

  return 0;
}