import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    long k = sc.nextLong();
    long[] a = new long[n];
    long[] b = new long[n];
    for(int i = 0; i < n; i++) {
      a[i] = sc.nextLong();
      b[i] = sc.nextLong();
    }
    long l = 1;
    long r = (long)Math.pow(10, 9) + 1;
    long ans = 0;
    while(l < r) {
      long med = (l + r) / 2;
      long t = 0;
      for(int i = 0; i < n; i++) {
        if(a[i] <= med) {
          if(b[i] <= med) {
            t += (b[i] - a[i] + 1);
          } else {
            t += (med - a[i] + 1);
          }
        }
      }
      if(t >= k) {
        ans = med;
        r = med;
      } else {
        l = med + 1;
      }
    }
    System.out.println(ans);
  }
}