Merge Two Dictionaries

You are given two dictionaries d1 and d2 in JSON format. Your task is to merge these dictionaries using the following rule:

• If a key exists in only one dictionary, include it with its corresponding value.
• If a key exists in both dictionaries, combine their values into a list. In particular, if a value is not already a list, treat it as a singleton list. Then, concatenate the lists. Formally, for any key k present in both dictionaries, the output should satisfy $$\text{output}[k] = \begin{cases} d1[k] & \text{if } k \notin d2, \\ d2[k] & \text{if } k \notin d1, \\ \text{List}(d1[k]) \oplus \text{List}(d2[k]) & \text{if } k \in d1 \text{ and } k \in d2, \end{cases}$$ where \(\text{List}(x)\) denotes x if x is already a list, and [x] otherwise, and \(\oplus\) denotes the list concatenation operation.

The merged dictionary must be output in JSON format.

inputFormat

The input consists of two lines read from standard input:

1. The first line is a JSON object representing the first dictionary d1.
2. The second line is a JSON object representing the second dictionary d2.

Each dictionary contains key-value pairs. Values can be integers, strings, or lists (of integers and/or strings).

outputFormat

Output a single JSON object that represents the merged dictionary, following the merging rules described above. The output should be printed to standard output.

{"a": 1, "b": "two"}
{"c": 3, "d": "four"}

{"a":1,"b":"two","c":3,"d":"four"}