North Korean leader Kim Jong Un smiles as he attends a flight training session by female fighter pilots Jo Kum Hyang and Rim Sol in this undated photo released by North Korea's Korean Central News Agency (KCNA) on June 22, 2015. (Photo by Reuters/KCNA/Antara Foto)

A house built on a rock on the river Drina is seen near the western Serbian town of Bajina Basta, about 160km (99 miles) from the capital Belgrade May 22, 2013. The house was built in 1968 by a group of young men who decided that the rock on the river was an ideal place for a tiny shelter, according to the house's co-owner, who was among those involved in its construction. (Photo by Marko Djurica/Reuters)

A reveller wearing a golden cape celebrates as the sun rises during the winter solstice at Stonehenge on Salisbury plain in southern England December 22, 2014. The winter solstice is the shortest day of the year, and the longest night of the year. (Photo by Dylan Martinez/Reuters)

A member of India’s Dongria tribe faints in trance during the two-day long Niyamraja Festival atop the Niyamgiri hills near Lanjigarh in Kalahandi district, Orissa state, India, Sunday, February 22, 2015. Every year, members of this indigenous group celebrate this festival sacrificing animals and birds in worship of their deity. (Photo by Biswaranjan Rout/AP Photo)

A Russian ground staff member signals to the pilot of a Sukhoi Su-25 fighter jet at the Hmeymim air base near Latakia, Syria, in this handout photograph released by Russia's Defence Ministry October 22, 2015. (Photo by Reuters/Ministry of Defence of the Russian Federation)

Collided passenger train cars are seen in Taebaek, South Korea, Tuesday, July 22, 2014. Two passenger trains collided head-on in eastern South Korea on Tuesday afternoon, killing one passenger and injuring dozens, fire officials said. (Photo by AFP Photo/Yonhap)