Everything got unclear to us in a far away constellation Tau Ceti. Specifically, the Taucetians choose names to their children in a very peculiar manner.

Two young parents abac and bbad think what name to give to their first-born child. They decided that the name will be the permutation of letters of string s. To keep up with the neighbours, they decided to call the baby so that the name was lexicographically strictly larger than the neighbour's son's name t.

On the other hand, they suspect that a name tax will be introduced shortly. According to it, the Taucetians with lexicographically larger names will pay larger taxes. That's the reason abac and bbad want to call the newborn so that the name was lexicographically strictly larger than name t and lexicographically minimum at that.

The lexicographical order of strings is the order we are all used to, the "dictionary" order. Such comparison is used in all modern programming languages to compare strings. Formally, a string p of length n is lexicographically less than string q of length m, if one of the two statements is correct:

  * n < m, and p is the beginning (prefix) of string q (for example, "aba" is less than string "abaa"), 
  * p1 = q1, p2 = q2, ..., pk - 1 = qk - 1, pk < qk for some k (1 ≤ k ≤ min(n, m)), here characters in strings are numbered starting from 1. 



Write a program that, given string s and the heighbours' child's name t determines the string that is the result of permutation of letters in s. The string should be lexicographically strictly more than t and also, lexicographically minimum.

Input

The first line contains a non-empty string s (1 ≤ |s| ≤ 5000), where |s| is its length. The second line contains a non-empty string t (1 ≤ |t| ≤ 5000), where |t| is its length. Both strings consist of lowercase Latin letters.

Output

Print the sought name or -1 if it doesn't exist.

Examples

Input

aad
aac


Output

aad


Input

abad
bob


Output

daab


Input

abc
defg


Output

-1


Input

czaaab
abcdef


Output

abczaa

Note

In the first sample the given string s is the sought one, consequently, we do not need to change the letter order there.
import java.awt.Point;
import java.io.*;
import java.math.BigInteger;
import java.util.*;
import static java.lang.Math.*;
 
public class D {
        
        final boolean ONLINE_JUDGE = System.getProperty("ONLINE_JUDGE")!=null;
        BufferedReader in;
        PrintWriter out;
        StringTokenizer tok = new StringTokenizer("");
        
        void init() throws FileNotFoundException{
                if (ONLINE_JUDGE){
                        in = new BufferedReader(new InputStreamReader(System.in));
                        out = new PrintWriter(System.out);
                }else{
                        in = new BufferedReader(new FileReader("input.txt"));
                        out = new PrintWriter("output.txt");
                }
        }
        
        String readString() throws IOException{
                while(!tok.hasMoreTokens()){
                        tok = new StringTokenizer(in.readLine());
                }
                return tok.nextToken();
        }
        
        int readInt() throws IOException{
                return Integer.parseInt(readString());
        }
        
        long readLong() throws IOException{
                return Long.parseLong(readString());
        }
        
        double readDouble() throws IOException{
                return Double.parseDouble(readString());
        }
        
        int[] readArr(int n) throws IOException{
        	int[] res = new int[n];
        	for(int i = 0; i < n; i++){
        		res[i] = readInt();
        	}
        	return res;
        }
        
        long[] readArrL(int n) throws IOException{
        	long[] res = new long[n];
        	for(int i = 0; i < n; i++){
        		res[i] = readLong();
        	}
        	return res;
        }
        
        public static void main(String[] args){
                new D().run();
        }
        
        public void run(){
                try{
                        long t1 = System.currentTimeMillis();
                        init();
                        solve();
                        out.close();
                        long t2 = System.currentTimeMillis();
                        System.err.println("Time = "+(t2-t1));
                }catch (Exception e){
                        e.printStackTrace(System.err);
                        System.exit(-1);
                }
        }        
        char[] s;
        char[] t;
        int[] num;
        int cl;
        char[] res;
        
        
        int dfs(int i){
        	if(i > s.length - 1){
        		return -1;
        	}
        	if(i > t.length - 1){
        		for(int j = 0; j < 26; j++){
        			if(num[j] != 0){
        				res[i] = (char)(j+'a');
                		return 1;
        			}
        		}
        	}
        	if(num[t[i]-'a'] == 0){
        		for(int j = t[i]+1; j < 26+'a'; j++){
        			if(num[j-'a'] != 0) {
        				res[i] = (char)(j);
        				return 1;
        			}
        		}
        		return -1;
        	}
        	num[t[i]-'a']--;
        	res[i] = (char)(t[i]);
        	int r = dfs(i+1);
        	num[t[i]-'a']++;
        	if(r == 0) return 0;
        	if(r == 1){
        		cl = i+1;
        		return 0;
        	}
        	if(r == -1){
        		for(int j = t[i]+1; j < 26+'a'; j++){
        			if(num[j-'a'] != 0) {
        				res[i] = (char)(j);
        				return 1;
        			}
        		}
        		return -1;
        	}
        	return -1;
        }
        
        void solve() throws IOException{
        	s = readString().toCharArray();
        	t = readString().toCharArray();
        	res = new char[s.length];
        	num = new int[26];
        	for(int i = 0; i < s.length; i++){
        		num[s[i]-'a']++;
        	}
        	int c = dfs(0);
        	if(c == -1){
        		out.println(-1);
        		return;
        	}
        	for(int i = 0; i <= cl; i++){
        		num[res[i] - 'a']--;
        	}
        	int k = cl+1;
        	for(int i = 0; i < 26; i++){
        		for(int j = 0; j < num[i]; j++){
        			res[k] = (char)(i + 'a');
        			k++;
        		}
        	}
        	out.println(new String(res));
        }
        
        void maxHepify(int[] a, int i, int length){
        	int l = (i<<1) + 1;
        	int r = (i<<1) + 2;
        	int largest = i;
        	if(l < length && a[l] > a[largest])
        		largest = l;
        	if(r < length && a[r] > a[largest])
        		largest = r;
        	if(largest != i){
        		a[largest] += a[i];
        		a[i] = a[largest] - a[i];
        		a[largest] -= a[i];
        		maxHepify(a, largest, length);
        	}
        }
        
        void buildMaxHeap(int[] a){
        	for(int i = a.length/2 - 1; i >= 0; i--){
        		maxHepify(a, i, a.length);
        	}
        }
        
        void heapSort(int[] a){
        	buildMaxHeap(a);
        	for(int i = a.length - 1; i > 0; i--){
        		a[i] += a[0];
        		a[0] = a[i] - a[0];
        		a[i] -= a[0];
        		maxHepify(a, 0, i);
        	}
        }

        
        int[] zFunction(char[] s){
        	int[] z = new int[s.length];
        	z[0] = 0;
        	for (int i=1, l=0, r=0; i<s.length; ++i) {
        		if (i <= r)
        			z[i] = min (r-i+1, z[i-l]);
        		while (i+z[i] < s.length && s[z[i]] == s[i+z[i]])
        			++z[i];
        		if (i+z[i]-1 > r){
        			l = i; 
        			r = i+z[i]-1;
        		}
        	}	
        	return z;
        }
        
        int[] prefixFunction(char[] s){
        	int[] pr = new int[s.length];
        	for (int i = 1; i< s.length; ++i) {
        		int j = pr[i-1];
        		while (j > 0 && s[i] != s[j])
        			j = pr[j-1];
        		if (s[i] == s[j])  ++j;
        		pr[i] = j;
        	}
        	return pr;
        }
        
        int ModExp(int a, int n, int mod){
        	int res = 1;
        	while (n!=0)
        		if ((n & 1) != 0) {
        			res = (res*a)%mod;
        			--n;
        		}
        		else {
        			a = (a*a)%mod;
        			n >>= 1;
        		}
        	return res;
        }
        
        
        public static class Utils {       	
 
        	private Utils() {}

        	public static void mergeSort(int[] a) {
                    mergeSort(a, 0, a.length - 1);
            }
             
        	private static void mergeSort(int[] a, int leftIndex, int rightIndex) {
                    final int MAGIC_VALUE = 50;
                    if (leftIndex < rightIndex) {
                            if (rightIndex - leftIndex <= MAGIC_VALUE) {
                                    insertionSort(a, leftIndex, rightIndex);
                            } else {
                                    int middleIndex = (leftIndex + rightIndex) / 2;
                                    mergeSort(a, leftIndex, middleIndex);
                                    mergeSort(a, middleIndex + 1, rightIndex);
                                    merge(a, leftIndex, middleIndex, rightIndex);
                            }
                    }
            }
 
            private static void merge(int[] a, int leftIndex, int middleIndex, int rightIndex) {
            	int length1 = middleIndex - leftIndex + 1;
            	int length2 = rightIndex - middleIndex;
                int[] leftArray = new int[length1];
                int[] rightArray = new int[length2];
                System.arraycopy(a, leftIndex, leftArray, 0, length1);
                System.arraycopy(a, middleIndex + 1, rightArray, 0, length2);
                for (int k = leftIndex, i = 0, j = 0; k <= rightIndex; k++) {
                    if (i == length1) {
                            a[k] = rightArray[j++];
                    } else if (j == length2) {
                            a[k] = leftArray[i++];
                    } else {
                            a[k] = leftArray[i] <= rightArray[j] ? leftArray[i++] : rightArray[j++];
                    }
                }
            }
 
            private static void insertionSort(int[] a, int leftIndex, int rightIndex) {
                for (int i = leftIndex + 1; i <= rightIndex; i++) {
            		int current = a[i];
                    int j = i - 1;
                	while (j >= leftIndex && a[j] > current) {
                        a[j + 1] = a[j];
                        j--;
                        }
                    a[j + 1] = current;
                }
            }
        }
        
         
       
        
        boolean isPrime(int a){
        	for(int i = 2; i <= sqrt(a); i++)
        		if(a % i == 0) return false;
        	return true;
        }
        
        static double distance(long x1, long y1, long x2, long y2){
        	return Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        }
        
        static long gcd(long a, long b){
        	if(min(a,b) == 0) return max(a,b);
        	return gcd(max(a, b) % min(a,b), min(a,b));
        }
        
        static long lcm(long a, long b){
        	return a * b /gcd(a, b);
        }
}

/*class Treap<K extends Comparable<K>>{
	
	public K x;
	public double y;
	public Treap<K> left;
	public Treap<K> right;
	
	public Treap(K x, double y, Treap<K> left, Treap<K> right) {
		this.x = x;
		this.y = y;
		this.left = left;
		this.right = right;
	}
	
	public static <K extends Comparable<K>> Treap<K> merge(Treap<K> l, Treap<K> r){
		if(l == null) return r;
		if(r == null) return l;
		if(l.y > r.y){
			return new Treap<K>(l.x, l.y, l.left, merge(l.right, r));
		}
		else{
			return new Treap<K>(r.x, r.y, merge(l, r.left), r.right);
		}
	}
	
	public void split(K x, Treap<K> left, Treap<K> right){
		Treap<K> newTreap = null;
		if(this.x.compareTo(x) <= 0){
			if(this.right == null){
				right = null;
			}
			else{
				right.split(x, newTreap, right);
			}
			left = new Treap<K>(this.x, this.y, left, newTreap);
		}
		else{
			if(this.left == null){
				left = null;
			}
			else{
				left.split(x, left, newTreap);
			}
			right = new Treap<K>(x, y, newTreap, right);
		}
	}
	
	public Treap<K> add(K x){
		Treap<K> left = null, right = null;
		this.split(x, left, right);
		Treap<K> temp = new Treap<K>(x, random(), null, null);
		return merge(merge(left, temp), right);
	}
	
	@SuppressWarnings("null")
	public Treap<K> remove(K x){
		Treap<K> left = null, temp = null, right = null;
		this.split(x, left, right);
		right.split(x, temp, right);
		return merge(left, right);
	}
	
	public static <K extends Comparable<K>> Treap<K> build(K[] a){
		Treap<K> temp = new Treap<K>(a[0], random(), null, null);
		for(int i = 1; i < a.length; i++){
			temp = temp.add(a[i]);
		}
		return temp;
	}
}*/