import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
        int[] aArr = new int[n];
        int[] bArr = new int[n];
        for (int i = 0; i < n; i++) {
            aArr[i] = sc.nextInt();
            bArr[i] = sc.nextInt();
        }
        int left = 0;
        int right = 1000000001;
        while (right - left > 1) {
            int m = (left + right) / 2;
            long sum = 0;
            for (int i = 0; i < n; i++) {
                sum += Math.max(Math.min(bArr[i], m) - aArr[i] + 1, 0);
            }
            if (sum <= k - 1) {
                left = m;
            } else {
                right = m;
            }
        }
        System.out.println(left + 1);
    }
}