import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.HashSet;
import java.util.NoSuchElementException;

public class Main {
	public static void main(String[] args) throws FileNotFoundException {
		long t = System.currentTimeMillis();
		new Main().run();
		System.err.println(System.currentTimeMillis() - t);
	}
	
	void run() {
		FastScanner sc = new FastScanner();
		HashSet<Integer> set=new HashSet<>();
		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();
			set.add(A[i]);
			set.add(B[i]);
			set.add(B[i]+1);
		}
		int[] dp=new int[set.size()];
		int[] val=new int[set.size()];
		int p=0;
		for(int v:set) {
			val[p++]=v;
		}
		Arrays.sort(val);
		for(int i=0;i<N;++i) {
			dp[Arrays.binarySearch(val, A[i])]++;
			dp[Arrays.binarySearch(val, B[i]+1)]--;
		}
		for(int i=1;i<dp.length;++i) {
			dp[i]+=dp[i-1];
		}
		long res=K,ans=0;
		p=0;
		while(res>0) {
			long gap=val[p+1]-val[p];
			if(res<=(long)dp[p]*gap) {
				ans=val[p]-1+(res+dp[p]-1)/dp[p];
				break;
			}else {
				res-=dp[p]*gap;
				++p;
			}
		}
		System.out.println(ans);
	}

	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}
	
	
class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
    public boolean hasNext() { skipUnprintable(); return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    
    public int nextInt() {
    	return (int)nextLong();
    }
}