Problem: Petya loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn't contain digits other than 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Lucky number is super lucky if it's decimal representation contains equal amount of digits 4 and 7. For example, numbers 47, 7744, 474477 are super lucky and 4, 744, 467 are not.

One day Petya came across a positive integer n. Help him to find the least super lucky number which is not less than n.

Input

The only line contains a positive integer n (1 ≤ n ≤ 10100000). This number doesn't have leading zeroes.

Output

Output the least super lucky number that is more than or equal to n.

Examples

Input

4500


Output

4747


Input

47


Output

47

Solution (in JAVA):

Solution:
    			/*
    		     * Author- Priyam Vora
    		     * BTech 2nd Year DAIICT
    		     */
    		     
    		            
    		    import java.io.*;
    		    import java.math.*;
    		    import java.util.*;
    		    import javax.print.attribute.SetOfIntegerSyntax;


    		     
    		    public class Practice{
    		    	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;
    		    	private static long count = 0,mod=1000000007;
    		    //	private static TreeSet<Integer> ts=new TreeSet[200000];
    		    
    		        public static void main(String[] args) {
    		        	InputReader(System.in);
    		    		pw = new PrintWriter(System.out); 
    		            new Thread(null ,new Runnable(){
    		               public void run(){
    		                   try{
    		                       soln2();
    		                       pw.close();
    		                   } catch(Exception e){
    		                       e.printStackTrace();
    		                   }
    		               }
    		           },"1",1<<26).start();
    		       }
    		    
    		    	public static long gcd(long x, long y) {
    		    		if (x == 0)
    		    			return y;
    		    		else
    		    			return gcd( y % x,x);
    		    	}
    		    	public static String reverseString(String s) {
    		    		StringBuilder sb = new StringBuilder(s);
    		    		sb.reverse();
    		    		return (sb.toString());
    		    	}
    		    	
    		    	public static long pow(long n, long p) {
    		    		if(p==0)
    		    			return 1;
    		    		if(p==1)
    		    			return n%mod;
    		    		if(p%2==0){
    		    			long temp=pow(n, p/2);
    		    		return (temp*temp)%mod;
    		    		}else{
    		    			 	long temp=pow(n,p/2);
    		    			 	temp=(temp*temp)%mod;
    		    			 	return(temp*n)%mod;
    		    			 	
    		    		}
    		    	}
    		     
    		    		
    		     
    		    	public static boolean isPrime(int n) {
    		    		// Corner cases
    		    		if (n <= 1)
    		    			return false;
    		    		if (n <= 3)
    		    			return true;
    		     
    		    		// This is checked so that we can skip 
    		    		// middle five numbers in below loop
    		    		if (n % 2 == 0 || n % 3 == 0)
    		    			return false;
    		     
    		    		for (int i = 5; i * i <= n; i = i + 6)
    		    			if (n % i == 0 || n % (i + 2) == 0)
    		    				return false;
    		     
    		    		return true;
    		    	}
    		     
    		    	// 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 nextInt() {
    		    		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 nextLong() {
    		    		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 nextLine() {
    		    		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[] nextIntArray(int n) {
    		    		int[] arr = new int[n];
    		    		for (int i = 0; i < n; i++) {
    		    			arr[i] = nextInt();
    		    		}
    		    		return arr;
    		    	}
    		     
    		    	private static int[][] next2dArray(int n, int m) {
    		    		int[][] arr = new int[n][m];
    		    		for (int i = 0; i < n; i++) {
    		    			for (int j = 0; j < m; j++) {
    		    				arr[i][j] = nextInt();
    		    			}
    		    		}
    		    		return arr;
    		    	}
    		    	private static char[][] nextCharArray(int n,int m){
    		    		char [][]c=new char[n][m];
    		    		for(int i=0;i<n;i++){
    		    			String s=nextLine();
    		    			for(int j=0;j<s.length();j++){
    		    				c[i][j]=s.charAt(j);
    		    			}
    		    		}
    		    		return c;
    		    	}
    		     
    		    	private static long[] nextLongArray(int n) {
    		    		long[] arr = new long[n];
    		    		for (int i = 0; i < n; i++) {
    		    			arr[i] = nextLong();
    		    		}
    		    		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 void pArray(boolean[] 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);
    		    	}



    		    	static ArrayList<Long> a;
    		    	private static void soln2(){

    		    		a=new ArrayList<Long>();
    		    		BFS(4);
    		    		BFS(7);
    		    	//	pw.println(a.size());
    		    		Collections.sort(a);
    		    		long n=nextLong();
    		    		int low=0,high=a.size()-1;
    		    		long ans=0;
    		    		while(low<=high){
    		    			int mid=(low+high)/2;
    		    			if(a.get(mid)<n){
    		    				low=mid+1;
    		    			}else{
    		    				ans=a.get(mid);
    		    				high=mid-1;
    		    			}
    		    		}
    		    		pw.println(ans);
    		    	//	pw.println(a.contains(4747));
    


    		    	}
    		    	private static void BFS(int startv){
    		    		Queue<String> q=new LinkedList<String>();
    		    		q.add(Long.toString(startv));
    		    		while(!q.isEmpty()){
    		    			String top=q.poll();
    		    			int no_4=0,no_7=0;
		    				for(int i=0;i<top.length();i++){
		    					if(top.charAt(i)=='4')
		    						no_4++;
		    					else
		    						no_7++;
		    				}

		    				if(no_4==no_7)
    		    			a.add(Long.parseLong(top));
    		    			if(Long.parseLong(top.concat("4"))<=(long)1e18){
    		    				String top2=top.concat("4");
    		    				
    		    				q.add(top.concat("4"));
    		    				
    		    			
    		    			}
    		    			if(Long.parseLong(top.concat("7"))<=(long)1e18){
    		    				String top2=top.concat("7");
    		    				
    		    				q.add(top.concat("7"));
    		    			}
    		    			}
    		    		
    		    	}
    		    }
    		    	class Pair implements Comparable<Pair>{
 	     			   
               	    	
        				long day,height;
        				Pair(long a,long b){
        				day=a;
        				height=b;
        				}
    					@Override
    					public int compareTo(Pair o) {
    						
  
    						return (int)(day-o.day);
//    					return (int)(mon-o.mon);
    					}
               		
        		    
    			/*	public int hashCode() {
					//	return 0;
    	    			int hu = (int) (row ^ (row >>> 32));
    	    			int hv = (int) (col ^ (col >>> 32));
    	    			return 31 * hu + hv;
    	    		}
    				public boolean equals(Object o) {
    	    			Pair other = (Pair) o;
    	    		return row == other.row && col == other.col;
    	    		}
    		*/
    		    	}
    		        class Graph{
    		        	private static int V,level[][],count=-1,lev_dfs[],degree=0,no_vert_conn_comp=0;
    		        	private Stack <Integer>st=new Stack();
    		        	private static LinkedList<Integer > adj[];
    		        	private boolean[][] Visite;
    		        	private static boolean [] Visited;
    		        	private static HashSet<Integer> Vis=new HashSet();
    		        	private static Stack<Integer> topo_sort=new Stack<>();
    		        	private static HashMap<String,Integer> hm=new HashMap<>();
    		  private static HashSet<String> hs=new HashSet();
    		private static HashSet<String > exist=new HashSet();
    		private static int a[];

    		
    		    Graph(int V){
    		    V++;
    		    this.V=(V);
    		    adj=new LinkedList[V];
    		    Visite=new boolean[100][100];
    		    
    	 	    Visited=new boolean[V];
    		    level=new int[100][100];
    		    lev_dfs=new int[V]; 
    		   for(int i=0;i<V;i++)
    			   adj[i]=new LinkedList<Integer>();
    		a=new int[V+1];
    		    }
    		   
    		    void setup(int d[]){
  
    		    	a=Arrays.copyOf(d, d.length);
    		    	
    		    }
    		    void ans(){
    		    	StringBuilder sb=new StringBuilder();
    		    	for(int i=1;i<a.length;i++){
    		    		sb.append(a[i]+" ");
    		    	}
    		    	System.out.println(sb);
    		    }
    		   void addEdge(int v,int w){
    		    
    		    	if(adj[v]==null){
    		    		adj[v]=new LinkedList();
    		    	}
    		    	adj[v].add(w);
    		    
    		    	
    		    
    		    	  	
    		    }
    		  
    		    public static int BFS2(int startVert){
    		    	Visited=new boolean[V];
    		    	for(int i=1;i<V;i++){
    		    		lev_dfs[i]=-1;
    		    	}
    		    //	System.out.println(startVert);
    		    	Queue<Integer> q=new LinkedList<Integer>();
    		    	q.add(startVert);
    		    	
    		    	lev_dfs[startVert]=0;
    		    	while(!q.isEmpty()){
    		    		int top=q.poll();
    		    		
    		    		Iterator<Integer> i= adj[top].listIterator();
    		    		while(i.hasNext()){
    		    			int n=i.next();
    		    	//		System.out.println(top+" "+n);
    		    			if(!Visited[n]){
    		    				q.add(n);
    		    				Visited[n]=true;
    		    				lev_dfs[n]=lev_dfs[top]+1;
    		    			
    		    			}
    		    		}
    		    	}
    		    
    		    //	q.clear();
    		    	return -1;
    		    }
    		    public static int getAn(){
    		    	if(ans==Long.MAX_VALUE)
    		    		ans=-1;
    		    	return 0;
    		    }
    		    public int getEd(){
    		    	return degree/2;
    		    }
    		    public void get(int from,int to){
    		    	int h=lev_dfs[from]-lev_dfs[to];
    		    	if(h<=0){
    		    		System.out.println(-1);
    		    	}else{
    		    		System.out.println(h-1);
    		    	}
    		    }
    		    private static boolean check(int x,int y,char c[][]){
    			
    				if((x>=0 && y>=0) && (x<c.length && y<c[0].length) && c[x][y]!='#'){
    					
    					return true;
    				}
    				return false;
    			}
    		    public int BFS(int x,int y,int k,char[][] c)
    		    {
    		    	 LinkedList<Pair> queue = new LinkedList<Pair>();
    		        //Visited[s]=true;
    		   //     queue.add(new Pair(x,y));
    		       int count=0;
    		   level[x][y]=-1;
    		   c[x][y]='M';
    		        while (!queue.isEmpty())
    		        {
    		            Pair temp = queue.poll();
    		        
    		            
    		        }
    		        return V;
    		    }
    		    static long ans=Long.MAX_VALUE;
    		    
    		   public static void dfs2(int startVert,int endVert,long need){
    			Visited[startVert]=true;
    			//System.out.println(startVert+" "+need);
    			   for(int x:adj[startVert]){
    				if(x==endVert ){
    					String to="";
    					to+=startVert+" "+x;
    					
    					if(hs.contains(to) && startVert!=x)
    					ans=Math.min(need+1, ans);
    					else
    						ans=Math.min(need, ans);
    				}
    				else{
    					String to="";
    					to+=startVert+" "+x;
    					boolean tmp=false;
    					if(hs.contains(to) )
    						tmp=true;
    					if(!Visited[x])
    					{
    					if(tmp)
    						dfs2(x, endVert, need+1);
    					else{
    						dfs2(x, endVert, need);
    					}
    					}
    					}
    			}
    			   
    			   
    		   }
    		     public long dfs(int startVertex){
    		    //	 getAns(startVertex);
    		    	 if(!Visited[startVertex])  {
    		    	
    		   return dfsUtil(startVertex);
    		  
    		    	//return getAns();
    		    	}
    		    	 
    		    
    		     
    		    return 0;
    		    	}
    		 private long dfsUtil(int startVertex) {//0-Blue 1-Pink
    			 int c=1;
    		TreeSet<Integer> index=new TreeSet();
    		TreeSet<Integer> ele=new TreeSet(Collections.reverseOrder());
    			 long cout=0;
    		      degree=0;
    		    	Visited[startVertex]=true;
    		    	lev_dfs[startVertex]=0;
    		      st.push(startVertex);
    		      int temp=-1;
    		    	    while(!st.isEmpty()){
    		    	
    		    	int top=st.pop();
    		    //	ts.add(top);
    		    	Iterator<Integer> i=adj[top].listIterator();

      		      index.add(top);
      		      ele.add(a[top]);
    		    while(i.hasNext()){
    		    //	System.out.println(top);
    		    	int n=i.next();
    		     if( !Visited[n]){
    		    				Visited[n]=true;
    		    				st.push(n);
    		    c++;
    		     }
    		         }
    		 }
    		    	   for(int x:index){
    		    		   a[x]=ele.first();
    		    		   ele.remove(ele.first());
    		    	  }
    		 
    		 //   System.out.println(temp);
    		    return 0;
    		    }
    		        
    		        }     
    		       	        
    		    class Dsu{
    		    	private int rank[], parent[] ,n;
    		    	private static int[] parent1;
    		    	Dsu(int size){
    		    		this.n=size+1;
    		    		rank=new int[n];
    		    		//parent=new int[n];
    		    		parent=new int[n];
    		    	makeSet();
    		
    		    	}
    		    	
    		    	void makeSet(){
    		    		for(int i=0;i<n;i++){
    		    			parent[i]=i;
    		    		}
    		    	}
    		    	
    		    	int find(int x){
    		    		if(parent[x]!=x){
    		    			
    		    			parent[x]=find(parent[x]);
    		    		}
    		    		return parent[x];
    		    	}
    		    
    		    	
    		    	void union(int x,int y){
    		    		int xRoot=find(x);
    		    		int yRoot=find(y);
    		    		
    		    		if(xRoot==yRoot)
    		    			return;
    		    		if(rank[xRoot]<rank[yRoot]){
    		    		parent[xRoot]=yRoot;	
    		    		}else if(rank[yRoot]<rank[xRoot]){
    		    			parent[yRoot]=xRoot;
    		    		}else{
    		    			parent[yRoot]=xRoot;
    		    			rank[xRoot]++;
    		    		}
    		    		
    		    	}

    		     
    		    }