// Linear rather than binary search; Moore's algorithm

import java.util.*;
import java.io.*;


public class TaxedRSR_slow {
  public static int n,m;
  public static int book[][];
  public static long lo, hi;
  public static final double EPS = 1e-10;

  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer(in.readLine());
    n = Integer.parseInt(st.nextToken());
    m = Integer.parseInt(st.nextToken());
    book = new int[n][2];
    double minratio = Double.MAX_VALUE;
    double maxratio = 0;
    for (int i = 0; i < n; i++) {
      st = new StringTokenizer(in.readLine());
      book[i][0] = Integer.parseInt(st.nextToken());
      book[i][1] = Integer.parseInt(st.nextToken());
      double r = 1.0*book[i][0]/book[i][1];
      if (r < minratio) minratio = r;
      if (r > maxratio) maxratio = r;
    }
    lo = (long)Math.ceil(minratio);
    hi = n*(long)Math.ceil(maxratio);
    // Sort by increasing deadline:
    Arrays.sort(book,Comparator.comparingInt(a->a[1]));

    long best = search(lo,hi,hi);
    System.out.println(best);
  }

  public static long search(long lo, long hi, long best) {
    for (long mid = lo; mid <= hi; mid++) {
      int late = moore(mid);
      if (late <= m) {
        return mid;
      }
    }
    return -1;
 }

  public static int moore(long rate) {
    // we need to be able to quickly find the longest running time of
    // a job, so...
    Comparator<Integer> runtime = new Comparator<Integer>() {
        // finds longer of two running times:
        public int compare(Integer i1, Integer i2) {
          return book[i2][0] - book[i1][0];
        }
      };

    PriorityQueue<Integer> jobs = new PriorityQueue<>(runtime);
    // Now run Moore's algorithm:
    int late = 0;
    long total = 0;
    for (int i = 0; i < n; i++) {
      jobs.add(i);
      long t = book[i][0];
      total += t;
      int remove = -1;
      while (remove != i && 1.0*total/rate > book[i][1]) {
        remove = jobs.poll();
        late++;
        total -= book[remove][0];
      }
    }
    return late;     
  }
}