Problem: There are n players sitting at a round table. All of them have s cards of n colors in total. Besides, initially the first person had cards of only the first color, the second one had cards of only the second color and so on. They can swap the cards by the following rules: 

  * as the players swap, a player can give a card of his color only; 
  * a player can't accept a card of a color he already has (particularly, he can't take cards of his color, no matter whether he has given out all of them or not); 
  * during one swap a pair of people swaps cards (each person gives one card and takes one card). 



The aim of all n people is as follows: each of them should give out all the cards he had initially (that is, all cards of his color). Your task is to denote whether such sequence of swaps is possible. If the answer is positive, you should list all the swaps.

Input

The first line contains integers n (1 ≤ n ≤ 200000) and s (1 ≤ s ≤ 200000). The second line contains n numbers, the i-th number stands for how many cards the i-th player has by the moment the game starts. It is possible that a player has no cards initially.

Output

On the first line print "No" if such sequence of swaps is impossible. Otherwise, print "Yes". If the answer is positive, next print number k — the number of the swaps. Then on k lines describe the swaps by pairs of indices of the swapping players. Print the swaps and the numbers of the swaps in any order.

Examples

Input

4 8
2 2 2 2


Output

Yes
4
4 3
4 2
1 3
1 2


Input

6 12
1 1 2 2 3 3


Output

Yes
6
6 5
6 4
6 3
5 4
5 3
2 1


Input

5 5
0 0 0 0 5


Output

No

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.ObjectInputStream.GetField;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.InputMismatchException;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Scanner;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;




	public class Q1 {
		
		static long MOD = 1000000007;
		static boolean b[], b1[], check;
		static ArrayList<Integer>[] amp, pa;
		static ArrayList<Pair>[] amp1;
		static ArrayList<Pair>[][] damp;
		static int left[],s[],right[],sum[],dist[],cnt[],start[],color[],parent[],prime[],size[];
		static long ans = 0,k;
		static int p = 0;
		static FasterScanner sc = new FasterScanner(System.in);
		static Queue<Pair> queue = new LinkedList<>();
		static PriorityQueue<Integer> pq;
		static BufferedWriter log;
		static HashSet<Integer>[] hs;
		static HashMap<String,Integer> hm;
		static HashMap<Pair,Integer> hmp;
		static Stack<Integer> st;
		static boolean boo[][];
		static Pair prr[];
		static long parent1[],parent2[],size1[],size2[],arr1[],SUM[],MAX[];
		static int arr[];
		public static void main(String[] args) throws Exception {
	    	/*new Thread(null, new Runnable() {
				public void run() {
					try {
*/
						soln();
	/*				} catch (Exception e) {
						System.out.println(e);
					}
				}
			}, "1", 1 << 26).start();
		*/}
		static Pair dp[][];
		static int N,K,T;
		static int time[][],cost[][];
		static boolean b11[];
		static HashMap<Pair,Integer> h = new HashMap<>();
		static long ans1;
		static long ans2;
		public static void soln() throws IOException {
			//FasterScanner in = new FasterScanner(new FileInputStream("C:\\Users\\Admin\\Desktop\\QCL.txt"));
			//PrintWriter out = new PrintWriter("C:\\Users\\Admin\\Desktop\\A1.txt");
			log = new BufferedWriter(new OutputStreamWriter(System.out));
			int n = sc.nextInt(), s = sc.nextInt();
			StringBuilder sb = new StringBuilder();
			int arr[] = sc.nextIntArray(n);
			Pair prr[] = new Pair[n+1];
			PriorityQueue<Pair> pq = new PriorityQueue<>(Collections.reverseOrder());
			
			prr[0] = new Pair(0,0);
			for(int i = 1;i<=n;i++){
				if(arr[i-1]>=n){
					System.out.println("No");
					return;
				}
				prr[i] = new Pair(arr[i-1],i);
				if(prr[i].u>0)
				pq.add(prr[i]);
			}
			if(s%2==1 || n==1){
				System.out.println("No");
				return;
			}
			else{
				sb.append("Yes\n");
				sb.append(s/2+"\n");
				int temp = 0;
				while(pq.size()>1){
					Pair p = pq.poll();
					temp = 0;
					for(int i = 0; i<p.u;i++){
						if(!pq.isEmpty()){
							prr[temp++] = pq.poll();
							sb.append(p.v+" "+prr[temp-1].v+"\n");
							prr[temp-1].u--;
						}
						else{
							System.out.println("No");return;
						}
					}
					for(int i = 0; i< temp;i++){
						if(prr[i].u>0)
						pq.add(prr[i]);
					}
					//System.out.println(pq);
				}
				System.out.println(sb);
			}
			log.close();
			//out.close();
		}
		static long comp(long n, long m){
			int l = Math.max(Long.toBinaryString(n).length(),Long.toBinaryString(m).length());
			System.out.println((m&(n^MAX[l]))+" "+(((m^MAX[l])&n)));
			return 2*((m&(n^MAX[l]))+(((m^MAX[l])&n)));
		}
		static void recur(String str, int i, int n) throws IOException{
			//System.out.println(str+" "+i+" "+n);
			String s = str+(char)(i+'a')+"";
			if(n==N){
				log.write(s+"\n");
				return;
			}
			if(b[i]){
				for(int j = 0;j<26;j++){
					//System.out.println(1);
					if(!b[j] && j!=('y'-'a')){
						//System.out.println(1);
						recur(s,j,n+1); 
					}
				}
			}
			else{
				for(int j = 0;j<26;j++){
					if(b[j]){
					//	System.out.println(2);
						recur(s,j,n+1); 
					}
				}
			}
		}
		static void dfs(int x){
			long sum = 0, max = Long.MIN_VALUE;
			b[x] = true;
			//System.out.println(amp[x].size());
			PriorityQueue<Long> pq=new PriorityQueue<>(10,Collections.reverseOrder());
			if(amp[x].size()>2) check = true;
			for(int i:amp[x]){
				if(!b[i]){
					parent[i] = x;
					dfs(i);
					sum+=SUM[i];
					max = Math.max(max, MAX[i]);
					pq.add(MAX[i]);
				}
			}
			SUM[x] = sum+arr[x];
			MAX[x] = Math.max(SUM[x],max);
			if(pq.size()>=2){
				ans = Math.max(ans, pq.poll()+pq.poll());
			}
			
		}
		public static void buildWeightedGraph(int n){
			for(int i =0 ;i< n; i++){
				int x = sc.nextInt(), y = sc.nextInt(), w = sc.nextInt();
				amp1[--x].add(new Pair(--y,w));
				amp1[y].add(new Pair(x,w));
			}
		}
		
		public static void seive(int n){
			b = new boolean[(n+1)];
			Arrays.fill(b, true);
			b[1] = false;
			for(int i = 2;i*i<=n;i++){
				if(b[i]){
					for(int p = 2*i;p<=n;p+=i){
						b[p] = false;
					}
				}
			}
			/*for(int i = 2;i<=n;i++){
				if(b[i]) prime[i] = i;
			}*/
		}
		
		static class Graph{
			int vertex;
			int weight;
			Graph(int v, int w){
				vertex = v;
				weight = w;
			}
		}
		static class Pair implements Comparable<Pair> {
			int u;
			int v;
			public Pair(){
				u = 0;
				v = 0;
			}
			public Pair(int u, int 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=" + u + ", v=" + v + "]";
			}
		}
		
		public static void buildGraph(int n){
			for(int i =0;i<n;i++){
				int x = sc.nextInt()-1, y = sc.nextInt()-1;
				amp[x].add(y);
				amp[y].add(x);
			}
		}
		
		
		public static int getParent(long x){
			while(parent[(int) x]!=x){
				parent[ (int) x] = parent[(int) parent[ (int) x]];
				x = parent[ (int) x];
			}
			return (int) x;
		}
		static long min(long a, long b, long c){
			if(a<b && a<c) return a;
			if(b<c) return b;
			return c;
		}
		/*
		
		static class Pair3{
			int x, y ,z;
			Pair3(int x, int y, int z){
				this.x = x;
				this.y = y;
				this.z = z;
			}
		}*/
		static int sum(int n){
			String str = Integer.toString(n);
			int cnt = 0;
			for(int i = 0; i< str.length();i++){
				cnt+=(str.charAt(i)-'0');
			}
			return cnt;
		}
		 static void KMPSearch(String pat, String txt)
		    {
		        int M = pat.length();
		        int N = txt.length();
		 
		        // create lps[] that will hold the longest
		        // prefix suffix values for pattern
		        int lps[] = new int[M];
		        int j = 0;  // index for pat[]
		 
		        // Preprocess the pattern (calculate lps[]
		        // array)
		        computeLPSArray(pat,M,lps);
		 
		        int i = 0;  // index for txt[]
		        while (i < N)
		        {
		            if (pat.charAt(j) == txt.charAt(i))
		            {
		                j++;
		                i++;
		            }
		            if (j == M)
		            {
		               // parent.add((i-j));
		                j = lps[j-1];
		            }
		 
		            // mismatch after j matches
		            else if (i < N && pat.charAt(j) != txt.charAt(i))
		            {
		                // Do not match lps[0..lps[j-1]] characters,
		                // they will match anyway
		                if (j != 0)
		                    j = lps[j-1];
		                else
		                    i = i+1;
		            }
		        }
		    }
		 static void computeLPSArray(String pat, int M, int lps[])
		    {
		        // length of the previous longest prefix suffix
		        int len = 0;
		        int i = 1;
		        lps[0] = 0;  // lps[0] is always 0
		 
		        // the loop calculates lps[i] for i = 1 to M-1
		        while (i < M)
		        {
		            if (pat.charAt(i) == pat.charAt(len))
		            {
		                len++;
		                lps[i] = len;
		                i++;
		            }
		            else  // (pat[i] != pat[len])
		            {
		                // This is tricky. Consider the example.
		                // AAACAAAA and i = 7. The idea is similar 
		                // to search step.
		                if (len != 0)
		                {
		                    len = lps[len-1];
		 
		                    // Also, note that we do not increment
		                    // i here
		                }
		                else  // if (len == 0)
		                {
		                    lps[i] = len;
		                    i++;
		                }
		            }
		        }
		    }
		private static void permutation(String prefix, String str) {
		    int n = str.length();
		    if (n == 0); //hs.add(prefix);
		    else {
		        for (int i = 0; i < n; i++)
		            permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i+1, n));
		    }
		}
		public static char give(char c1,char c2){
			if(c1!='a' && c2!='a') return 'a';
			if(c1!='b' && c2!='b') return 'b';
			return 'c';
		}
		
		public static void buildTree(int n){
			int arr[] = sc.nextIntArray(n);
			for(int i = 0;i<n;i++){
				int x = arr[i]-1;
				amp[i+1].add(x);
				amp[x].add(i+1);
			}
		}
		
		static class SegmentTree {
			boolean st[];
			boolean lazy[];

			SegmentTree(int n) {
				int size = 4 * n;
				st = new boolean[size];
				Arrays.fill(st, true);
				lazy = new boolean[size];
				Arrays.fill(lazy, true);
				//build(0, n - 1, 1);
			}
			
			/*long[] build(int ss, int se, int si) {
				if (ss == se) {
					st[si][0] = 1;
					st[si][1] = 1;
					st[si][2] = 1;
					return st[si];
				}
				int mid = (ss + se) / 2;
				long a1[] = build(ss, mid, si * 2), a2[] = build(mid + 1, se,
						si * 2 + 1);
				long ans[] = new long[3];
				if (arr[mid] < arr[mid + 1]) {
					ans[1] = Math.max(a2[1], Math.max(a1[1], a1[2] + a2[0]));
					if (a1[1] == (mid - ss + 1))
						ans[0] = ans[1];
					else
						ans[0] = a1[0];
					if (a2[2] == (se - mid))
						ans[2] = ans[1];
					else
						ans[2] = a2[2];
				} else {
					ans[1] = Math.max(a1[1], a2[1]);
					ans[0] = a1[0];
					ans[2] = a2[2];
				}
				st[si] = ans;
				return st[si];
			}*/

			void update(int si, int ss, int se, int idx, long x) {
				if (ss == se) {
					//arr[idx] += val;
					st[si]=false;
				} 
				else {
					int mid = (ss + se) / 2;
					if(ss <= idx && idx <= mid)
			        {
			             update(2*si, ss, mid, idx, x);
			        }
			        else
			        { update(2*si+1, mid+1, se, idx, x);
			        }
					st[si] = st[2*si]|st[2*si+1];
				}
			}
			/*boolean get(int qs, int qe, int ss, int se, int si){
				if(qs>se || qe<ss) return 0;
				if (qs <= ss && qe >= se) {
					return st[si];
				}
				int mid = (ss+se)/2;
				return get(qs, qe, ss, mid, si * 2)+get(qs, qe, mid + 1, se, si * 2 + 1);
			}*/
			void updateRange(int node, int start, int end, int l, int r, boolean val)
			{
			    if(!lazy[node])
			    { 
			        // This node needs to be updated
			        st[node] = lazy[node];    // Update it
			        if(start != end)
			        {
			            lazy[node*2] = lazy[node];                  // Mark child as lazy
			            lazy[node*2+1] = lazy[node];                // Mark child as lazy
			        }
			        lazy[node] = true;                                  // Reset it
			    }
			    if(start > end || start > r || end < l)              // Current segment is not within range [l, r]
			        return;
			    if(start >= l && end <= r)
			    {
			        // Segment is fully within range
			        st[node] =  val;
			        if(start != end)
			        {
			            // Not leaf node
			            lazy[node*2] = val;
			            lazy[node*2+1] = val;
			        }
			        return;
			    }
			    int mid = (start + end) / 2;
			    updateRange(node*2, start, mid, l, r, val);        // Updating left child
			    updateRange(node*2 + 1, mid + 1, end, l, r, val);   // Updating right child
			    st[node] = st[node*2] | st[node*2+1];        // Updating root with max value 
			}

			boolean queryRange(int node, int start, int end, int l, int r)
			{
			    if(start > end || start > r || end < l)
			        return false;         // Out of range
			    if(!lazy[node])
			    {
			        // This node needs to be updated
			        st[node] = lazy[node];            // Update it
			        if(start != end)
			        {
			            lazy[node*2] = lazy[node];         // Mark child as lazy
			            lazy[node*2+1] = lazy[node];    // Mark child as lazy
			        }
			        lazy[node] = true;                 // Reset it
			    }
			    if(start >= l && end <= r)             // Current segment is totally within range [l, r]
			        return  st[node];
			    int mid = (start + end) / 2;
			    boolean p1 = queryRange(node*2, start, mid, l, r);         // Query left child
			    boolean b = queryRange(node*2 + 1, mid + 1, end, l, r); // Query right child
			    return (p1 | b);
			}
			void print() {
				for (int i = 0; i < st.length; i++) {
					System.out.print(st[i]+" ");
				}
				System.out.println();
			}
		}
		static int convert(int x){
			int cnt = 0;
			String str = Integer.toBinaryString(x);
			//System.out.println(str);
			for(int i = 0;i<str.length();i++){
				if(str.charAt(i)=='1'){
					cnt++;
				}
			}
			int ans = (int) Math.pow(3, 6-cnt);
			return ans;
		}
		static class Node2{
			Node2 left = null;
			Node2 right = null;
			Node2 parent = null;
			int data;
		}
		static class BinarySearchTree{
			Node2 root = null;
			int height = 0;
			int max = 0;
			int cnt = 1;
			ArrayList<Integer> parent = new ArrayList<>();
			HashMap<Integer, Integer> hm = new HashMap<>();
			public void insert(int x){
				Node2 n = new Node2();
				n.data = x;
				if(root==null){
					root = n;
				}
				else{
					Node2 temp = root,temb = null;
					while(temp!=null){
						temb = temp;
						if(x>temp.data) temp = temp.right;
						else temp = temp.left;
					}
					if(x>temb.data) temb.right = n;
					else temb.left = n;
					n.parent = temb;
					parent.add(temb.data);
				}
			}
			public Node2 getSomething(int x, int y, Node2 n){
				if(n.data==x || n.data==y) return n;
				else if(n.data>x && n.data<y) return n;
				else if(n.data<x && n.data<y) return getSomething(x,y,n.right);
				else return getSomething(x,y,n.left);
			}
			public Node2 search(int x,Node2 n){
				if(x==n.data){
					max = Math.max(max, n.data);
					return n;
				}
				if(x>n.data){
					max = Math.max(max, n.data);
					return search(x,n.right);
				}
				else{
					max = Math.max(max, n.data);
					return search(x,n.left);
				}
			}
			public int getHeight(Node2 n){
				if(n==null) return 0;
				height = 1+ Math.max(getHeight(n.left), getHeight(n.right));
				return height;
			}
		}
		static long findDiff(long[] arr, long[] brr, int m){
			int i = 0, j = 0;
			long fa = 1000000000000L;
			while(i<m && j<m){
				long x = arr[i]-brr[j];
				if(x>=0){
					if(x<fa) fa = x;
					j++;
				}
				else{
					if((-x)<fa) fa = -x;
					i++;
				}
			}
			return fa;
		}
		public static long max(long x, long y, long z){
			if(x>=y && x>=z) return x;
			if(y>=x && y>=z) return y;
			return z;
		}
		
		static long modInverse(long a, long mOD2){
		            return  power(a, mOD2-2, mOD2);
		}
		static long power(long x, long y, long m)
		{
		    if (y == 0)
		        return 1;
		    long p = power(x, y/2, m) % m;
		    p = (p * p) % m;
		 
		    return (y%2 == 0)? p : (x * p) % m;
		}
		static long power2(long x,BigInteger y,long m){
			long ans = 1;
			BigInteger two = new BigInteger("2");
			while(y.compareTo(BigInteger.ZERO)>0){
				if(y.getLowestSetBit()==y.bitCount()){
					x = (x*x)%MOD;
					y = y.divide(two);
				}
				else{
					ans = (ans*x)%MOD;
					y = y.subtract(BigInteger.ONE);
				}
			}
			return ans;
		}
		static BigInteger power2(BigInteger x, BigInteger y, BigInteger m){
			BigInteger ans = new BigInteger("1");
			BigInteger one  = new BigInteger("1");
			BigInteger two  = new BigInteger("2");
			BigInteger zero  = new BigInteger("0");
			while(y.compareTo(zero)>0){
				//System.out.println(y);
				if(y.mod(two).equals(one)){
					ans = ans.multiply(x).mod(m);
					y = y.subtract(one);
				}
				else{
					x = x.multiply(x).mod(m);
					y = y.divide(two);
				}
			}
			return ans;
		}
		static BigInteger power(BigInteger x, BigInteger y, BigInteger m)
		{
		    if (y.equals(0))
		        return (new BigInteger("1"));
		    BigInteger p = power(x, y.divide(new BigInteger("2")), m).mod(m);
		    p = (p.multiply(p)).mod(m);
		 
		    return (y.mod(new BigInteger("2")).equals(0))? p : (p.multiply(x)).mod(m);
		}
		static long d,x,y;
		public static void extendedEuclidian(long a, long b){
			if(b == 0) {
		        d = a;
		        x = 1;
		        y = 0;
		    }
		    else {
		        extendedEuclidian(b, a%b);
		        int temp = (int) x;
		        x = y;
		        y = temp - (a/b)*y;
		    }
		}
		
		public static long gcd(long n, long m){
			if(m!=0) return gcd(m,n%m);
			else return n;
		}
		
		static BufferedReader reader;
	    static StringTokenizer tokenizer;
	    static PrintWriter writer;
	
	
	   
	    static class FasterScanner {

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

			public FasterScanner(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] = nextInt();
				}
				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);
			}
		}
	}