Transpose a Negative Number to Positive and Vice Versa

I am wanting to be able to enter in a number in one cell and then have it's negative equivalent appear in another cell or enter a negative number in a cell and have its positive equivalent appear in another cell. Example: I enter the negative number (11.5) in F4 and I want the positive number 11.5 to then also appear in F10.

Or I enter the positive number 2.5 in F5 and I want the negative number (2.5) to appear in F12.

I can attach a sample worksheet if that would help.