A plane is flying at a constant height of h meters above the ground surface. Let's consider that it is flying from the point (-10^9, h) to the point (10^9, h) parallel with Ox axis.

A glider is inside the plane, ready to start his flight at any moment (for the sake of simplicity let's consider that he may start only when the plane's coordinates are integers). After jumping from the plane, he will fly in the same direction as the plane, parallel to Ox axis, covering a unit of distance every second. Naturally, he will also descend; thus his second coordinate will decrease by one unit every second.

There are ascending air flows on certain segments, each such segment is characterized by two numbers x_1 and x_2 (x_1 < x_2) representing its endpoints. No two segments share any common points. When the glider is inside one of such segments, he doesn't descend, so his second coordinate stays the same each second. The glider still flies along Ox axis, covering one unit of distance every second. 

<image> If the glider jumps out at 1, he will stop at 10. Otherwise, if he jumps out at 2, he will stop at 12.

Determine the maximum distance along Ox axis from the point where the glider's flight starts to the point where his flight ends if the glider can choose any integer coordinate to jump from the plane and start his flight. After touching the ground the glider stops altogether, so he cannot glide through an ascending airflow segment if his second coordinate is 0.

Input

The first line contains two integers n and h (1 ≤ n ≤ 2⋅10^{5}, 1 ≤ h ≤ 10^{9}) — the number of ascending air flow segments and the altitude at which the plane is flying, respectively.

Each of the next n lines contains two integers x_{i1} and x_{i2} (1 ≤ x_{i1} < x_{i2} ≤ 10^{9}) — the endpoints of the i-th ascending air flow segment. No two segments intersect, and they are given in ascending order.

Output

Print one integer — the maximum distance along Ox axis that the glider can fly from the point where he jumps off the plane to the point where he lands if he can start his flight at any integer coordinate.

Examples

Input

3 4
2 5
7 9
10 11


Output

10


Input

5 10
5 7
11 12
16 20
25 26
30 33


Output

18


Input

1 1000000000
1 1000000000


Output

1999999999

Note

In the first example if the glider can jump out at (2, 4), then the landing point is (12, 0), so the distance is 12-2 = 10.

In the second example the glider can fly from (16,10) to (34,0), and the distance is 34-16=18.

In the third example the glider can fly from (-100,1000000000) to (1999999899,0), so the distance is 1999999899-(-100)=1999999999.
import java.util.*;
import java.io.*;
import java.math.BigInteger;

public class D
{

    static int mod = (int) (1e9+7);
    static InputReader in;
    static PrintWriter out;
    
    
    static void solve() 
    {
        in = new InputReader(System.in);
        out = new PrintWriter(System.out); 
        
        int n = in.nextInt();
        long h = in.nextInt();
        
        long[][] x = new long[n][2];
        long[] sum = new long[n];
        
        for(int i = 0; i < n; i++) {
            x[i][0] = in.nextInt();
            x[i][1] = in.nextInt();
            if(i > 0) {
                sum[i] = sum[i - 1] + x[i][0] - x[i - 1][1];
            }
        }
        
        long ans = 0;
        
        for(int i = 0; i < n; i++) {
            int l = i;
            int r = n - 1;
            int idx = -1;
            while(r - l >= 0) {
                int m = (r + l) >> 1;
                if(sum[m] - sum[i] < h) {
                    idx = m;
                    l = m + 1;
                }
                else r = m - 1;
            }
//            debug(i,idx,(x[idx][1] - x[i][0]) + h - (sum[idx] - sum[i]));
            ans = Math.max(ans,(x[idx][1] - x[i][0]) + h - (sum[idx] - sum[i]));
        }
        
        out.println(ans);
        out.close(); 
    }
    
    static long add(long a, long b) {
        return (a + b) % mod;
    }
    
    static long mul(long a, long b) {
        return (a * b) % mod;
    }
    
    static long sub(long a, long b) {
        return (a - b + mod) % mod;
    } 
    
    public static void main(String[] args)
    {
        new Thread(null ,new Runnable(){
            public void run()
            {
                try{
                    solve();
                } catch(Exception e){
                    e.printStackTrace();
                }
            }
        },"1",1<<26).start();
    }
    
    static class Pair implements Comparable<Pair>
    {

        int x,y;
        int i;
        
        Pair (int x, int y)
        {
                this.x = x;
                this.y = y;
        }

        public int compareTo(Pair o)
        {
            return -Integer.compare(this.x, o.x);
        }

        public boolean equals(Object o)
        {
            if (o instanceof Pair)
            {
                Pair p = (Pair)o;
                return p.x == x && p.y==y;
            }
            return false;
        }

        @Override
        public String toString()
        {
            return x + " "+ y + " "+i;
        }

        /*public int hashCode()
        {
            return new Long(x).hashCode() * 31 + new Long(y).hashCode();
        }*/

    } 

    
    static String rev(String s){
        StringBuilder sb=new StringBuilder(s);
        sb.reverse();
        return sb.toString();
    }
    
    static long gcd(long x,long y)
    {
        if(y==0)
                return x;
        else
                return gcd(y,x%y);
    }

    static int gcd(int x,int y)
    {
        if(y==0)
                return x;
        else 
                return gcd(y,x%y);
    }

    static long pow(long n,long p,long m)
    {
         long  result = 1;
          if(p==0){
            return 1;
          }
          
        while(p!=0)
        {
            if(p%2==1)
                result *= n;
            if(result >= m)
               result %= m;
            p >>=1;
            n*=n;
            if(n >= m)
                n%=m;
        }
        
        return result;
    }

    static long pow(long n,long p)
    {
        long  result = 1;
          if(p==0)
            return 1;

        while(p!=0)
        {
            if(p%2==1)
                result *= n;	    
            p >>=1;
            n*=n;	    
        }
        return result;
    }

    static void debug(Object... o)
    {
            System.out.println(Arrays.deepToString(o));
    }

    static class InputReader
    {

        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, snumChars;
        private SpaceCharFilter filter;

        public InputReader(InputStream stream)
        {
                this.stream = stream;
        }

        public int snext()
        {
                if (snumChars == -1)
                        throw new InputMismatchException();
                if (curChar >= snumChars)
                {
                        curChar = 0;
                        try
                        {
                                snumChars = stream.read(buf);
                        } catch (IOException e)
                        {
                                throw new InputMismatchException();
                        }
                        if (snumChars <= 0)
                                return -1;
                }
                return buf[curChar++];
        }

        public int nextInt()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                int sgn = 1;
                if (c == '-')
                {
                        sgn = -1;
                        c = snext();
                }
                int res = 0;
                do
                {
                        if (c < '0' || c > '9')
                                throw new InputMismatchException();
                        res *= 10;
                        res += c - '0';
                        c = snext();
                } while (!isSpaceChar(c));
                return res * sgn;
        }

        public long nextLong()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                int sgn = 1;
                if (c == '-')
                {
                        sgn = -1;
                        c = snext();
                }
                long res = 0;
                do
                {
                        if (c < '0' || c > '9')
                                throw new InputMismatchException();
                        res *= 10;
                        res += c - '0';
                        c = snext();
                } while (!isSpaceChar(c));
                return res * sgn;
        }

        public int[] nextIntArray(int n)
        {
                int a[] = new int[n];
                for (int i = 0; i < n; i++)
                {
                        a[i] = nextInt();
                }
                return a;
        }

        public long[] nextLongArray(int n)
        {
                long a[] = new long[n];
                for (int i = 0; i < n; i++)
                {
                        a[i] = nextLong();
                }
                return a;
        }

        public String readString()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                StringBuilder res = new StringBuilder();
                do
                {
                        res.appendCodePoint(c);
                        c = snext();
                } while (!isSpaceChar(c));
                return res.toString();
        }

        public String nextLine()
        {
                int c = snext();
                while (isSpaceChar(c))
                        c = snext();
                StringBuilder res = new StringBuilder();
                do
                {
                        res.appendCodePoint(c);
                        c = snext();
                } while (!isEndOfLine(c));
                return res.toString();
        }

        public boolean isSpaceChar(int c)
        {
                if (filter != null)
                        return filter.isSpaceChar(c);
                return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        private boolean isEndOfLine(int c)
        {
                return c == '\n' || c == '\r' || c == -1;
        }

        public interface SpaceCharFilter
        {
                public boolean isSpaceChar(int ch);
        }

    }
}    
