#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<pair<int, int> > a, ans;
  int n, k, x, y;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    scanf("%d%d", &x, &y);
    a.push_back(pair<int, int>(x, -1));
    a.push_back(pair<int, int>(y, 1));
  }
  sort(a.begin(), a.end());
  int cnt = 0;
  pair<int, int> t;
  for (int i = 0; i < 2 * n; i++) {
    if (cnt == k - 1 && a[i].second == -1)
      x = a[i].first;
    else if (cnt == k && a[i].second == 1)
      ans.push_back(pair<int, int>(x, a[i].first));
    a[i].second == -1 ? cnt++ : cnt--;
  }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++)
    cout << ans[i].first << " " << ans[i].second << endl;
  return 0;
}
