Martin O'Neill could line up in a number of different ways to nullify the Italian threat
The maths is simple. Win against Italy tonight and Ireland go through to the knockout stage of a European Championship. Lose and we go home after three matches.
The maths may be simple but the choice of systems is far from simple and it's a headache for Martin O'Neill to ponder.
Based on the first two rounds in Group E at Euro 2016, Italy have used a system with three (outstanding) central defenders flanked by full-backs and protected in front by a midfield trio.
Even if some key players are rested, beating the defensive system is the problem.
There is a good chance O'Neill could go for a 4-2-3-1 formation with width in the side provided by natural wingers as below.
Going through the middle against Italy did not work out well for Belgium in the opening week of action. Thus Aiden McGeady and James McClean on either flank supported by the natural attacking instincts Seamus Coleman and Robbie Brady could help overload the Italian wing-backs and stretch the game.
Jeff Hendrick's inclusion would provide more attacking energy and runs from deep in comparison to the under-par James McCarthy, while Glenn Whelan would sit deep and protect.
The 4-2-3-1 is a common system in world football but a 5-3-2 (or 3-5-2 in attack) would mirror the opposition formation.
Width would be provided by the wing-backs, while The Gentleman Ultra's Richard Hall has highlighted the potential for Robbie Keane to operate in pockets.
But Ireland's record- goalscorer can only operate in a two and a back-five provides more balance in that regard than a straight 4-4-2.
The disadvantage with such a radical shift is the fact that it's a system rarely used by the Boys in Green over the years.
But the back-three/back-five, is one that Ray Houghton, for one, has called for because it suits the attacking instincts of Brady and Coleman while still allowing for the deployment of an extra defender.
Off the Ball is live from Lille tonight from 7pm with best of build-up and reaction as Ireland get set for a crucial game against Italy.