import java.util.Scanner;
import java.util.TreeMap;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		int[] a = new int[n];
		int[] b = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
			b[i] = sc.nextInt();
		}
		sc.close();

		TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
		for (int i = 0; i < n; i++) {
			if (map.containsKey(a[i])) {
				map.put(a[i], map.get(a[i]) + 1);
			} else {
				map.put(a[i], 1);
			}
			if (map.containsKey(b[i] + 1)) {
				map.put(b[i] + 1, map.get(b[i] + 1) - 1);
			} else {
				map.put(b[i] + 1, -1);
			}
		}

		int prev = 0;
		for (int key : map.keySet()) {
			prev = map.get(key) + prev;
			map.put(key, prev);
		}

		int prevK = map.firstKey();
		long prevV = map.get(prevK);
		map.pollFirstEntry();
		long cnt = 0;
		for (int key : map.keySet()) {
			if (cnt + prevV * (key - prevK) >= k) {
				long x = (k - 1 - cnt) / prevV + prevK;
				System.out.println(x);
				break;
			} else {
				cnt += prevV * (key - prevK);
				prevK = key;
				prevV = map.get(prevK);
			}
		}
	}
}