It's Euro 2016 maths timepublished at 18:05
In a way, Wales' task is simple. Win and they are in the knockout stages of the European Championship. (They can even top the group if England do not beat Slovakia)
But fail and we might have to get our calculators out. Well the calculators on our phones. Do people still carry calculators around? Did they ever? Anyway, I digress...
A draw for Wales will be good enough to secure a top-two place... as long as Slovakia do not beat England (a game which kicks off at the same time).
Teams level on points are separated by head-to-head record, and not goal difference. Wales beat Slovakia 2-1 in their opener so if they finish level on points, it's Wales who finish higher.
However, if Wales lose, they will drop out of the top two and automatic qualification spots (with Russia still able to qualify). If Chris Coleman's side lose and Slovakia do not, then they will finish bottom of the group, and can book their flights home.
BUT, there is a bit more to it than that...
Image source, Getty Images