package chelper;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.TreeSet;

import io.InputReader;
import io.OutputWriter;
import misc.SimpleSavingChelperSolution;


public class CHEFKO extends SimpleSavingChelperSolution {

  public static final Comparator<int[]> COMPARATOR = (o1, o2) -> {
    for (int i = 0; i < 3; i++) {
      int t = Integer.compare(o1[i], o2[i]);
      if (t != 0) {
        return t;
      }
    }
    return 0;
  };

  public void solve(int testNumber, InputReader in, OutputWriter out) {
    wrapSolve(testNumber, in, out);
  }

  @Override
  public void solve(int testNumber) {
    int n = in.nextInt();
    int k = in.nextInt();

    int[][] a = new int[n][2];
    List<int[]> events = new ArrayList<>();
    for (int i = 0; i < n; i++) {
      a[i][0] = in.nextInt();
      a[i][1] = in.nextInt();

      events.add(new int[]{a[i][0], -2, i});
      events.add(new int[]{a[i][1], +2, i});
    }

    events.sort(COMPARATOR);

    int maxLength = 0;

    TreeSet<int[]> left = new TreeSet<>(COMPARATOR);
    TreeSet<int[]> right = new TreeSet<>(COMPARATOR);

    for (int ei = 0; ei < events.size(); ) {
      int t = events.get(ei)[0];

      while (ei < events.size() && events.get(ei)[0] == t && events.get(ei)[1] == -2) {
        int i = events.get(ei)[2];
        int[] key = {a[i][0], -2, i};

        if (left.size() < k) {
          left.add(key);
        } else {
          right.add(key);
        }

        ei++;
      }

      if (events.get(ei)[0] == t && events.get(ei)[1] == +2 && left.size() == k) {
        maxLength = Math.max(maxLength, t - left.last()[0]);
      }

      while (ei < events.size() && events.get(ei)[0] == t && events.get(ei)[1] == +2) {
        int i = events.get(ei)[2];
        int[] key = {a[i][0], -2, i};

        if (left.contains(key)) {
          left.remove(key);

          if (!right.isEmpty()) {
            left.add(right.pollFirst());
          }
        } else {
          right.remove(key);
        }

        ei++;
      }

    }

    out.println(maxLength);
  }
}