CF909A.Generate Login

The preferred way to generate user login in Polygon is to concatenate a prefix of the user's first name and a prefix of their last name, in that order. Each prefix must be non-empty, and any of the prefixes can be the full name. Typically there are multiple possible logins for each person.

You are given the first and the last name of a user. Return the alphabetically earliest login they can get (regardless of other potential Polygon users).

As a reminder, a prefix of a string s is its substring which occurs at the beginning of s: "a", "ab", "abc" etc. are prefixes of string "{abcdef}" but "b" and 'bc" are not. A string a is alphabetically earlier than a string b, if a is a prefix of b, or a and b coincide up to some position, and then a has a letter that is alphabetically earlier than the corresponding letter in b: "a" and "ab" are alphabetically earlier than "ac" but "b" and "ba" are alphabetically later than "ac".

在 Polygon 中，生成用户登录名的首选方法是按顺序拼接用户名字的前缀和姓氏的前缀。每个前缀都必须非空，且任一前缀均可为对应名字或姓氏的完整字符串。通常，每个人可能对应多个不同的登录名。

现给定一个用户的名（first name）与姓（last name）。请返回该用户所能得到的字典序最小的登录名（不考虑其他潜在的 Polygon 用户）。

需要提醒的是：字符串 $s$ 的一个前缀是指其位于 $s$ 开头的子串，例如 "a"、"ab"、"abc" 等均为字符串 {abcdef} 的前缀，而 "b" 和 "bc" 则不是。字符串 $a$ 在字典序上早于字符串 $b$，当且仅当：$a$ 是 $b$ 的前缀；或者 $a$ 与 $b$ 在某个位置之前完全相同，而在该位置上 $a$ 对应的字母在字典序上早于 $b$ 对应的字母。例如 "a" 和 "ab" 在字典序上均早于 "ac"，而 "b" 和 "ba" 在字典序上则晚于 "ac"。

The input consists of a single line containing two space-separated strings: the first and the last names. Each character of each string is a lowercase English letter. The length of each string is between 1 and 10, inclusive.

输入包含一行，其中包含两个由空格分隔的字符串：名和姓。每个字符串的每个字符均为小写英文字母。每个字符串的长度在 $1$ 到 $10$ 之间（含端点）。

Output a single string — alphabetically earliest possible login formed from these names. The output should be given in lowercase as well.

输出一个字符串——由这些名字构成的字典序最小的登录名。输出结果也应为小写形式。