Replacing Digits

**题目描述** 给你一个由$n$个数字组成的整数$a$和长度为$m$的数字序列$s$（就是输入一个数字$a$和一个数字序列$s$）,序列s的位置j（1<=j<=m）中的数字表示您可以选择$a$中的任意位置i（1<=i<=n），并用$s_{j}$替换所选位置i中的数字。序列s中的每个元素最多只能参与一个替换操作。 您的任务是这样替换序列，使给定的数字$a$得到最大值。允许不使用$s$中的所有元素。

You are given an integer $ a $ that consists of $ n $ digits. You are also given a sequence of digits $ s $ of length $ m $ . The digit in position $ j $ ( $ 1<=j<=m $ ) of sequence $ s $ means that you can choose an arbitrary position $ i $ ( $ 1<=i<=n $ ) in $ a $ and replace the digit in the chosen position $ i $ with $ s_{j} $ . Each element in the sequence $ s $ can participate in no more than one replacing operation. Your task is to perform such sequence of replacements, that the given number $ a $ gets maximum value. You are allowed to use not all elements from $ s $ .

The first line contains positive integer $ a $ . Its length $ n $ is positive and doesn't exceed $ 10^{5} $ . The second line contains sequence of digits $ s $ . Its length $ m $ is positive and doesn't exceed $ 10^{5} $ . The digits in the sequence $ s $ are written consecutively without any separators. The given number $ a $ doesn't contain leading zeroes.

Print the maximum value that can be obtained from $ a $ after a series of replacements. You are allowed to use not all elements from $ s $ . The printed number shouldn't contain any leading zeroes.

1024
010

1124

987
1234567

987