import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        long k = sc.nextInt();
        int[] lows = new int[n];
        int[] highs = new int[n];
        for (int i = 0; i < n; i++) {
            lows[i] = sc.nextInt();
            highs[i] = sc.nextInt();
        }
        long left = 0;
        long right = Integer.MAX_VALUE / 2;
        while (right - left > 1) {
            long m = (left + right) / 2;
            long current = 0;
            for (int i = 0; i < n && current < k; i++) {
                if (highs[i] <= m) {
                    current += highs[i] - lows[i] + 1;
                } else if (lows[i] <= m) {
                    current += m - lows[i] + 1;
                }
            }
            if (current < k) {
                left = m;
            } else {
                right = m;
            }
        }
        System.out.println(right);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}