Once all five pairs are illuminated, after a random length of time (one to nine seconds), the red lights are turned off by the race director, at which point the race starts. The race length is defined as the smallest number of complete laps that exceeds 305 kilometers (the Monaco Grand Prix is the sole exception with a race length of 78 laps / 260.5 km), though occasionally some races are truncated due to special circumstances. The race can not exceed two hours in length; if this interval is reached the race will be ended at the end of the next full lap. The only exception is if the race is halted by a Red flag in which case the total time including the red flag stoppage must not exceed 4 hours (since 2012), and the total time excluding the red flag stoppage may not exceed 2 hours. Since the 2007 season, teams are supplied by the sole tyre supplier (currently Pirelli which replaced Bridgestone in 2011), and receive two different types of slick dry tyre compounds: "Prime" tyres (now either the Hard, Medium or Soft compound), and "Option" tyres (either the Medium, Soft or Supersoft compound). In 2016 teams received three different types of slick tyre. The Prime tyres are more durable than the Option tyres, however the Option tyres produce faster lap times than the Prime tyres (the Option tyres are said to be one second per lap quicker than the Prime tyres, though this figure varies between circuits). From 2014, drivers who qualify in the top ten must start the race with the tyres they used in the second qualifying session (previously this had been the tyres they used in the final qualifying session); all other drivers have freedom over which tyres they can start with. Each driver is also required to use both types of dry compound during a dry race, and so must make a mandatory pit-stop. Timing pitstops with reference to other cars is crucial—if they are following another car but are unable to pass, the driver may try to stay on the track as long as possible, or pit immediately, as newer tyres are usually faster. Prior to the 2010 season, drivers used to make pitstops for fuel more than once during a race, as the cars on average consumed two kilometres per litre (approximately five miles per gallon)- nowadays this figure is lower, due to changes in engines from 2014. From 2010, refuelling has been forbidden during a race. At the end of the race, the first, second and third-placed drivers take their places on a podium, where they stand as the national anthem of the race winner's home country and that of his team is played.