You are given two strings `s` and `t`.
String `t` is generated by randomly shuffling string `s` and then adding **one more letter** at a random position.
Return the letter that was added to `t`.
Example 1
Input:s = "abcd", t = "abcde"
Output:"e"
Explanation:'e' is the letter that was added.
Example 2
Input:s = "", t = "y"
Output:"y"
Example 3
Input:s = "a", t = "aa"
Output:"a"
Explanation:A second copy of an existing letter counts as the added letter.
Constraints
- 0 <= s.length <= 1000
- t.length == s.length + 1
- s and t consist of lowercase English letters.