user
Instruction
Answer the question based on the provided table.


Table
Table Title: List of law clerks of the Supreme Court of the United States (Seat 6)
Table Content:
| Clerk | Started | Finished | School (year) | Previous clerkship |
| --- | --- | --- | --- | --- |
| Kenneth W. Dam | 1957 | 1958 | Chicago (1957) | none |
| Alan C. Kohn | 1957 | 1958 | Wash U (1955) | none |
| William C. Canby, Jr. | 1958 | 1959 | Minnesota (1956) | none |
| Heywood H. Davis | 1958 | 1959 | Kansas (1958) | none |
| Jerome B. Libin | 1959 | 1960 | Michigan (1959) | none |
| Patrick F. McCartan | 1959 | 1960 | Notre Dame (1959) | none |
| D. Lawrence Gunnels | 1961 | 1962 | Wash U (1960) | none |


Question
how long was kenneth w. dam's clerkship?


Answer Format
The final answer should be concise and use the following format:
```json
{
    "answer": [
        "answer1",
        "answer2",
        ...
    ]
}
```
rule
["1 year"]