On her way to programming school tiger Dasha faced her first test — a huge staircase!

<image>

The steps were numbered from one to infinity. As we know, tigers are very fond of all striped things, it is possible that it has something to do with their color. So on some interval of her way she calculated two values — the number of steps with even and odd numbers. 

You need to check whether there is an interval of steps from the l-th to the r-th (1 ≤ l ≤ r), for which values that Dasha has found are correct.

Input

In the only line you are given two integers a, b (0 ≤ a, b ≤ 100) — the number of even and odd steps, accordingly.

Output

In the only line print "YES", if the interval of steps described above exists, and "NO" otherwise.

Examples

Input

2 3


Output

YES


Input

3 1


Output

NO

Note

In the first example one of suitable intervals is from 1 to 5. The interval contains two even steps — 2 and 4, and three odd: 1, 3 and 5.
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.*;
import java.util.Map.Entry;

public class TestClass {
	private static InputStream stream;
	private static byte[] buf = new byte[1024];
	private static int curChar;
	private static int numChars;
	private static SpaceCharFilter filter;
	private static PrintWriter pw;
	
	public static class Queue{
		private class node{
			int val;
			node next;
			node(int a){
				val = a;
				next = null;
			}
		}
		node head,tail;
		Queue(){
			head = null;
			tail = null;
		}
		public void EnQueue(int a){
			if(head==null){
				node p = new node(a);
				head = p;
				tail = p;
			}
			else{
				node p = new node(a);
				tail.next = p;
				tail = p;
			}
		}
		public int DeQueue(){
			int a = head.val;
			head = head.next;
			return a;
		}
		public boolean isEmpty(){
			return head==null;
		}
	}
	public static long pow(long x,long y,long m){
		if(y==0)
    		return 1;
    	long k = pow(x,y/2,m);
    	if(y%2==0)
    		return (k*k)%m;
    	else
    		return (((k*k)%m)*x)%m;
    }
	static long Inversex = 0,Inversey = 0;
	public static void InverseModulo(long a,long m){
		if(m==0){
			Inversex = 1;
			Inversey = 0;
		}
		else{
    		InverseModulo(m,a%m);
    		long temp = Inversex;
    		Inversex = Inversey;
    		Inversey = temp+ - (a/m)*Inversey;
    	}
    }
    static long mod1 = 1000000007;
    static long mod2 = 1000000009;
	public static long gcd(long a,long b){
		if(a%b==0)
			return b;
		return gcd(b,a%b);
	}
	public static boolean isPrime(long a){
		if(a==1)
			return false;
		else if(a==2||a==3)
			return true;
		for(long i=2;i<=Math.sqrt(a);i++)
			if(a%i==0)
				return false;
		return true;
	}
	public static double distance(int a,int b,int x,int y){
		return Math.sqrt(((long)(a-x)*(long)(a-x))+((long)(b-y)*(long)(b-y)));
	}
	public static class Pair implements Comparable<Pair> {
		long u;
		long v;
		public Pair(long u, long v) {
			this.u = u;
			this.v = v;
		}
		public int hashCode() {
			int hu = (int) (u ^ (u >>> 32));
			int hv = (int) (v ^ (v >>> 32));
			return 31 * hu + hv;
		}
		public boolean equals(Object o) {
			Pair other = (Pair) o;
			return u == other.u && v == other.v;
		}
		public int compareTo(Pair other) {
			return Long.compare(u, other.u) != 0 ? Long.compare(u, other.u) : Long.compare(v, other.v);
		}
		public String toString() {
			return u+" "+v;
		}
	}
	public static class Pairs implements Comparable<Pairs> {
		long u;
		long v;
		int id;
		public Pairs(long u, long v,int w) {
			this.u = u;
			this.v = v;
			this.id = w;
		}
		public int hashCode() {
			int hu = (int) (u ^ (u >>> 32));
			int hv = (int) (v ^ (v >>> 32));
			return 31 * hu + hv;
		}
		public boolean equals(Object o) {
			Pairs other = (Pairs) o;
			return u == other.u && v == other.v;
		}
		public int compareTo(Pairs other) {
			return Long.compare(u, other.u) != 0 ? Long.compare(u, other.u) : Long.compare(v, other.v);
		}
		public String toString() {
			return u+" "+v;
		}
	}
	public static int sieve(int a[],boolean b[]){
		int count = 0;
		b[0] = true;
		b[1] = true;
		for(int i=2;i<a.length;i++){
			if(!b[i]){
				for(int j=2*i;j<a.length;j=j+i){
					b[j] = true;	
				}
				a[count++] = i;
			}
		}
		return count;
	}
	public static void MatrixMultiplication(int a[][],int b[][],int c[][]){
		for(int i=0;i<a.length;i++){
			for(int j=0;j<b[0].length;j++){
				c[i][j] = 0;
				for(int k=0;k<b.length;k++)
					c[i][j]=(int)((c[i][j]+((a[i][k]*(long)b[k][j])%mod1))%mod1);
			}
		}
	}
	public static void Equal(int arr[][],int temp[][]){
		for(int i=0;i<arr.length;i++){
			for(int j=0;j<arr.length;j++)
				temp[i][j] = arr[i][j];
		}
	}
	public static void makeHash(String a,long b[],long mod){
		for(int i=1;i<=a.length();i++)
			b[i] = ((a.charAt(i-1)-'a')+b[i-1]*26)%mod;
	}
	/*public static long getHash(long b[],int p,int q,long mod){
		
	}
	public static void Merge(long a[][],int p,int r){
        if(p<r){
            int q = (p+r)/2;
            Merge(a,p,q);
            Merge(a,q+1,r);
            Merge_Array(a,p,q,r);
        }
    }
	public static void get(long a[][],long b[][],int i,int j){
		for(int k=0;k<a[i].length;k++)
			a[i][k] = b[j][k];
	}
    public static void Merge_Array(long a[][],int p,int q,int r){
        long b[][] = new long[q-p+1][a[0].length];
        long c[][] = new long[r-q][a[0].length];
        for(int i=0;i<b.length;i++){
            get(b,a,i,p+i);
        }
        for(int i=0;i<c.length;i++){
            get(c,a,i,q+i+1);
        }
        int i = 0,j = 0;
        for(int k=p;k<=r;k++){
            if(i==b.length){
                get(a,c,k,j);
                j++;
            }
            else if(j==c.length){
                get(a,b,k,i);
                i++;
            }
            else if(b[i][0]<c[j][0]){
                get(a,b,k,i);
                i++;
            }
            else{
                get(a,c,k,j);
                j++;
            }
        }
    }
    public static void powMatrix(long n){
    	if(n<=1)
    		return ;
    	powMatrix(n/2);
    	MatrixMultiplication(temp2,temp2,result);
		Equal(result,temp2);
    	if(n%2==1){
    		MatrixMultiplication(temp2,a,result);
    		Equal(result,temp2);
    	}
    }
    static int result[][] = new int[4][4];
	static int temp[][] = new int[4][4];
	static int temp2[][] = new int[4][4];
	static int a[][] = new int[4][4];
	static int[][] b = new int[4][1];
	static int [][] c = new int[4][1];
    public static int count(long n){
		a[0][0] = 1 ;
		a[0][1] = 1;
		a[1][0] = 1;
		a[2][1] = 1;
		a[3][0] = 1;
		a[3][1] = 1;
		a[3][3] = 1;
		b[0][0] = 1;
		b[1][0] = 1;
		b[2][0] = 0;
		b[3][0] = 2;
		Equal(a,temp2);
		result[0][0] = 1;
		result[1][1] = 1;
		result[2][2] = 1;
		result[3][3] = 1;
		Equal(result,temp);
		if(n<=0)
			return 0;
		else if(n==1)
			return 1;
		else if(n==2)
			return 2;
		n = n-2;
		powMatrix(n);
		MatrixMultiplication(temp2,b,c);
		return c[3][0];
	}*/
	public static class ST{
		int arr[] = new int[800000];
		int lazy[] = new int[800000];
		//int zero[] = new int[800000];
		ST(int a[]){
			Build(a,0,a.length-1,0);
		}
		public void Build(int a[],int p,int q,int count){
			if(p==q){
				arr[count] = a[p];
				//zero[count] = 1;
				return ;
			}
			int mid = (p+q)/2;
			Build(a,p,mid,2*count+1);
			Build(a,mid+1,q,2*count+2);
			arr[count] = arr[2*count+1]&arr[2*count+2];
			//zero[count] = zero[2*count+1]+zero[2*count+2];
		}
		public void print(){
			for(int i=0;i<10;i++)
				pw.print(arr[i]+" ");
			pw.println();
		}
		public int getSum(int p,int q,int x,int y,int count){
			if(lazy[count]!=0){
				arr[count]|=lazy[count];
				lazy[2*count+1]|=lazy[count];
				lazy[2*count+2]|=lazy[count];
				lazy[count] = 0;
			}
			if(q<x||p>y||p>q){
				//pw.println("UT");
				return (int)Math.pow(2, 30)-1;
			}
			else if(x<=p&&y>=q){
				//pw.println(count+" UT "+arr[count]);
				return arr[count];
			}
			int mid = (p+q)/2;
			return getSum(p,mid,x,y,2*count+1)&getSum(mid+1,q,x,y,2*count+2);
		}
		public void Update(int p,int q,int x,int y,int count,int up){
			if(lazy[count]!=0){
				arr[count]|=lazy[count];
				lazy[2*count+1]|=lazy[count];
				lazy[2*count+2]|=lazy[count];
				lazy[count] = 0;
				//pw.println("UTSAV");
			}
			if(q<x||p>y||p>q)
				return;
			else if(x<=p&&y>=q){
				arr[count]|=up;
				lazy[2*count+1]|=up;
				lazy[2*count+2]|=up;
				return ;
			}
			int mid = (p+q)/2;
			Update(p,mid,x,y,2*count+1,up);
			Update(mid+1,q,x,y,2*count+2,up);
			arr[count] = arr[2*count+1]&arr[2*count+2];
		}
	}
	public static class Trie{
		Node head;
		private class Node{
			Node a[] = new Node[26];
			Node(){
				for(int i=0;i<26;i++)
					a[i] = null;
			}
			boolean u,v;
		}
		Trie(){
			head = null;
		}
		public void insert(String a,int p,Node kl){
			if(p==a.length())
				return ;
			if(kl==null){
				Node k = new Node();
				head = k;
				k.a[a.charAt(p)-'a'] = new Node();
				insert(a,p+1,k.a[a.charAt(p)-'a']);
			}
			else{
				if(kl.a[a.charAt(p)-'a']==null)
					kl.a[a.charAt(p)-'a'] = new Node();
				insert(a,p+1,kl.a[a.charAt(p)-'a']);
			}
		}
		public void fix(Node kl){
			boolean temp = false;
			for(int i=0;i<26;i++){
				if(kl.a[i]!=null){
					if(!kl.a[i].v)
						fix(kl.a[i]);
					temp|=kl.a[i].u;
				}
			}
			kl.v = true;
			kl.u = !temp;
		}
		public void pfix(Node kl){
			boolean temp = false;
			int count = 0;
			for(int i=0;i<26;i++){
				if(kl.a[i]!=null){
					if(kl.a[i].v)
						pfix(kl.a[i]);
					temp|=kl.a[i].u;
				}
				else
					count++;
			}
			kl.v = false;
			if(count==26)
				kl.u = false;
			else
				kl.u = !temp;
		}
	}
	private static void soln(){
		/*String a = nLi();
		String b = nLi();
		int x[] = new int[b.length()],y[] = new int[b.length()];
		int count = 0;
		for(int i=0;i<a.length();i++){
			if(count==b.length())
				break;
			if(a.charAt(i)==b.charAt(count))
				x[count++] = i+1;
		}
		int count2 = b.length()-1;
		for(int i=a.length()-1;i>=0;i--){
			if(count2==-1)
				break;
			if(a.charAt(i)==b.charAt(count2))
				y[count2--] = i+1;
		}
		int max = Integer.MIN_VALUE;
		Pair p = new Pair(0,b.length());
		if(x[0]==0&&y[0]==0){
			pw.println("-");
			return ;
		}
		count2++;
		pw.println(count+" "+count2);
		for(int i=0;i<count;i++){
			if(count2==b.length()){
				p.u = i+1;
				continue;
			}
			if(x[i]+1-y[count2]<=0){
				if(max<x[i]+1-y[count2]){
					max = x[i]+1-y[count2];
					p.u = x[i];
					p.v = y[count2]-1;
				}
			}
			else{
				i--;
				count2++;
			}
		}
		for(int i=0;i<p.u;i++)
			pw.print(b.charAt(i));
		for(int i=(int)p.v;i<b.length();i++)
			pw.print(b.charAt(i));*/
		/*int n = nI();
		int l = nI();
		int a1[] = new int[n],a2[] = new int[n];
		int arr[] = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = nI();
		for(int i=1;i<n;i++)
			a1[i] = arr[i]-arr[i-1];
		a1[0] = (l+arr[0])-arr[n-1];
		Arrays.sort(a1);
		for(int i=0;i<n;i++)
			arr[i] = nI();
		for(int i=1;i<n;i++)
			a2[i] = arr[i]-arr[i-1];
		a2[0] = (l+arr[0])-arr[n-1];
		Arrays.sort(a2);
		for(int i=0;i<n;i++){
			if(a1[i]!=a2[i]){
				pw.println("NO");
				return ;
			}
		}
		pw.println("YES");*/
		int e = nI();
		int o = nI();
		if(e==0&&o==0){
			pw.println("NO");
			return ;
		}
		if(Math.abs(e-o)<=1)
			pw.println("YES");
		else
			pw.println("NO");
	}
	public static void main(String[] args) {
		InputReader(System.in);
		pw = new PrintWriter(System.out);
		soln();
		pw.close();
	}
	// To Get Input
	// Some Buffer Methods
	public static void InputReader(InputStream stream1) {
		stream = stream1;
	}
	private static boolean isWhitespace(int c) {
		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
	}
	private static boolean isEndOfLine(int c) {
		return c == '\n' || c == '\r' || c == -1;
	}
	private static int read() {
		if (numChars == -1)
			throw new InputMismatchException();
		if (curChar >= numChars) {
			curChar = 0;
			try {
				numChars = stream.read(buf);
			} catch (IOException e) {
				throw new InputMismatchException();
			}
			if (numChars <= 0)
				return -1;
		}
		return buf[curChar++];
	}
	private static int nI() {
		int c = read();
		while (isSpaceChar(c))
			c = read();
		int sgn = 1;
		if (c == '-') {
			sgn = -1;
			c = read();
		}
		int res = 0;
		do {
			if (c < '0' || c > '9')
				throw new InputMismatchException();
			res *= 10;
			res += c - '0';
			c = read();
		} while (!isSpaceChar(c));
		return res * sgn;
	}
	private static long nL() {
		int c = read();
		while (isSpaceChar(c))
			c = read();
		int sgn = 1;
		if (c == '-') {
			sgn = -1;
			c = read();
		}
		long res = 0;
		do {
			if (c < '0' || c > '9')
				throw new InputMismatchException();
			res *= 10;
			res += c - '0';
			c = read();
		} while (!isSpaceChar(c));
		return res * sgn;
	}
	private static String nextToken() {
		int c = read();
		while (isSpaceChar(c))
			c = read();
		StringBuilder res = new StringBuilder();
		do {
			res.appendCodePoint(c);
			c = read();
		} while (!isSpaceChar(c));
		return res.toString();
	}
	private static String nLi() {
		int c = read();
		while (isSpaceChar(c))
			c = read();
		StringBuilder res = new StringBuilder();
		do {
			res.appendCodePoint(c);
			c = read();
		} while (!isEndOfLine(c));
		return res.toString();
	}
	private static int[] nIA(int n) {
		int[] arr = new int[n];
		for (int i = 0; i < n; i++)
			arr[i] = nI();
		return arr;
	}
	private static long[] nLA(int n) {
		long[] arr = new long[n];
		for (int i = 0; i < n; i++)
			arr[i] = nL();
		return arr;
	}
	private static void pArray(int[] arr) {
		for (int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
		pw.println();
		return;
	}
	private static void pArray(long[] arr) {
		for (int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
		pw.println();
		return;
	}
	private static boolean isSpaceChar(int c) {
		if (filter != null)
			return filter.isSpaceChar(c);
		return isWhitespace(c);
	}
	private interface SpaceCharFilter {
		public boolean isSpaceChar(int ch);
	}
}