Doofish matrix problem is copied

I found that doofish matrix is a copy of a problem from IMO 1997.
I found this out yesterday around 10 am but at that point i decided to not report it since many users including me who solved this problem on their own would be at a huge loss if it was removed or replaced, especially with only a few hours left on the clock.
@admin @vijju123 :sweat_smile: