Help me Open the Box

I have an ASCII-art box and I need a program to open it.

Examples

Input:

-------
|     |
|_____|

Output:

      /
     /
    /
   /
  /
 /
/
|     |
|_____|

Specification

  • The first line will only consist of -, at least 3 of them
  • The middle rows will start with | have spaces, and end with |
    • All the middle rows will be the same
  • The last row will start with | have _ and end with a |
  • All rows will be the same length

Opening the box:

  • Each - should be replaced by a / in ascending lines and position.

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