only one runner finishes the right marathon course,

Bungling organisers of the Marathon of the North have been forced to apologise after 5,000 runners ended up running 264m short of marathon distance because of a blunder by race marshalls.
Only the winner, Jake Harrison, completed the correct course in Sunderland.
But Harrison had built up a sufficient lead of the race that the vehicles following him were out of sight.
The second- and third-placed runners headed off in the wrong direction, and that meant that everyone thereafter did not complete the full distance.
For those runners who fell short of the 26.2 mile route, it meant that all their months of training and effort did not result in a complete marathon.