It was never going to be easy.

With 24 teams in the group stages at Euro 2016, that does not divide neatly into 16 qualifying for the knockout stages.

The best four third-placed teams from the six groups progress to the last 16.

So far, 12 teams have made it through: France, Switzerland, Wales, England, Slovakia, Germany, Poland, Spain, Croatia, Italy, Hungary and Northern Ireland.

BBC Sport helps explain which sides can still go through, why yellow cards could prove crucial and who is in pole position in the 'third-place table'.

Group-by-group: Who is going through and who is going home?

The Republic must win to stand any chance of qualifying, although Martin O'Neill's team - currently bottom of the table - may have to settle for third place.

Belgium will finish second with a draw against Sweden, who will ensure the runners-up spot themselves with a victory - unless the Republic win as well and, in doing so, also finish with a better goal difference. That is a challenge because Sweden enter the final round of group matches level on points with the Republic, but with a goal difference advantage of two.

There is an outside chance that the Republic and Sweden could finish level for second on points, head-to-head record, goal difference and goals scored if both win. If that happens fair play records will come into play. Going into the final round of group matches, Sweden have a marginally better fair play record.

What happens if teams finish level on points?

The top two teams from each group qualify automatically for the last 16, but how are sides separated if they finish on the same number of points?

The final position of teams will be decided by these criteria, in the following order:

• Head-to-head record in the group
• Points in the match(es) between the teams in question
• Goal difference in those matches
• Goals scored in those matches
• If teams still have an equal ranking, the criteria are reapplied but only to matches between the teams in question to determine their final rankings. This only applies if there are more than two teams level on points
• If teams are still level, it comes down to goal difference in all group matches, followed by goals scored, fair play conduct in the group stage, and finally Uefa national team coefficient rankings

Who is likely to finish third in each group?

Group A: Albania beat Romania on Sunday to secure third spot.

Group B: Slovakia drew with England to finish in third place.

Group C: Northern Ireland were beaten by Germany but finished third.

Group D: Turkey beat the Czech Republic to finish third.

Group E: One of Republic of Ireland, Sweden or Belgium. Republic of Ireland must get a better result against Italy than Sweden manage against Belgium. If Ireland and Sweden both win, second place will come down to goal difference between those two teams, while Belgium go out. If Ireland and Sweden both lose, goal difference will determine who finishes third and who is fourth. Belgium will finish third if they lose to Sweden and the Republic do not beat Italy.

Group F: Portugal are currently third and will probably stay there unless they beat group leaders Hungary. If Portugal do win, Hungary will be relying on the result of the game between Iceland and Austria; an Iceland win would relegate Hungary to third; a draw would leave Iceland third; while an Austria win would keep Hungary second and send Iceland out.

What about that third-placed table?

We know that the top two teams go through, but what happens to those third-placed teams? Remember only four can go through from six.

The following Uefa criteria will be applied, in this order:

• Points tally
• Goal difference
• Goals scored
• Fair play ranking in the group stage
• Uefa national team coefficient rankings (These are based on all competitive results since September 2010. England are ranked third overall but Republic of Ireland are 20th of the 24 finalists, Wales are 22nd and Northern Ireland 24th)