comment and uncomment code inline

It's very useful to be able to comment out a block of code in a quick edit. And likewise to uncomment the code. This operation often involves multi-line stanzas and even large blocks. With just line-wise navigation and insert mode this would cost you about 4 keystrokes per line. Master this hole of VimGolf and you'll quickly drop your key count in day to day Vim as well.

Input

These first three lines should
be commented out with C-style
inline comments.

// These three lines should have
// the C-style insline comment 
// characters removed.

Output

// These first three lines should
// be commented out with C-style
// inline comments.

These three lines should have
the C-style insline comment 
characters removed.