Early attempts to breed Tasmanian devils in captivity had limited success. Mary Roberts bred a pair at Beaumaris Zoo which she named Billy and Truganini in 1913. However, although advised to remove Billy, Roberts found Truganini too distressed by his absence, and returned him. The first litter was presumed eaten by Billy, but a second litter in 1914 survived after Billy was removed. Roberts wrote an article on keeping and breeding the devils for the London Zoological Society. Even by 1934, successful breeding of the devil was rare. In a study on the growth of young devils in captivity, some developmental stages were very different from those reported by Guiler. The pinnae were free on day 36, and eyes opened later, on days 115–121.In general, females tend to retain more stress after being taken into captivity than males.A plan to create "insurance populations" of disease-free devils has been ongoing since 2005. As of June 2012, the insurance population has reached a combined total of 500 animals and representing over 98% of the genetic diversity of this species. Most of these devils are living in Australian zoos and wildlife reserves. Beginning in November 2012 however, in an effort to create a population that is both wild and disease-free, Tasmanian devils have been relocated to Maria Island, a mountainous island off the east coast of Tasmania. The Maria Island population has grown from a starting population of twenty-eight to 90 and experts will soon begin transferring healthy devils back to the mainland population.  A study on the survival rates of the Maria Island population found that in contrast to other carnivores raised in captivity, the Tasmanian devils were not adversely affected by being born in captivity when released on Maria Island.Tasmanian devils were displayed in various zoos around the world from the 1850s onwards. In the 1950s several animals were given to European zoos. In October 2005 the Tasmanian government sent four devils, two male and two female, to the Copenhagen Zoo, following the birth of the first son of Frederik, Crown Prince of Denmark and his Tasmanian-born wife Mary. Due to restrictions on their export by the Australian government, at the time these were the only devils known to be living outside Australia. In June 2013, due to the successes of the insurance population program, it was planned to send devils to other zoos around the world in a pilot program. San Diego Zoo Global and Albuquerque Biopark were selected to participate in the program, and Wellington Zoo and Auckland Zoo soon followed. In the United States, four additional zoos have since been selected as part of the Australian government's Save the Tasmanian Devil program, the zoos selected were: the Fort Wayne Children's Zoo, the Los Angeles Zoo, the Saint Louis Zoo, and the Toledo Zoo. Captive devils are usually forced to stay awake during the day to cater to visitors, rather than following their natural nocturnal style.There have been reports and suspicions of illegal trading in the past. In 1997, a devil turned up in Western Australia; it had not escaped from any licensed keeper. During the 1990s there were internet sites in the US that were advertising devil sales, and rumours that some US Navy personnel had tried to buy them illegally during a visit to Tasmania.

Question: How many Tasmanian devils were sent to the Copenhagen Zoo by the Tasmanian government?
Answer: four