Passage: Tymoshenko has worked as a practicing economist and academic. Prior to her political career, she became a successful but controversial businesswoman in the gas industry, becoming by some estimates one of the richest people in the country. Before becoming Ukraine's first female prime minister in 2005, Tymoshenko co-led the Orange Revolution. She was placed third in Forbes magazine's List of The World's 100 Most Powerful Women 2005.After graduating from the Dnipropetrovsk State University in 1984, Tymoshenko worked as an engineer-economist in the "Dnipro Machine-Building Plant" (which produced missiles) in Dnipropetrovsk until 1988.In 1988, as part of the perestroika initiatives, Yulia and Oleksandr Tymoshenko borrowed 5000 Soviet rubles and opened a video-rental cooperative, perhaps with the help of Oleksander's father, Gennadi Tymoshenko, who presided over a regional film-distribution network in the provincial council.From 1989 to 1991, Yulia and Oleksandr Tymoshenko founded and led a commercial video-rental company "Terminal" in Dnipropetrovsk,In 1991, Tymoshenko established (jointly with her husband Oleksandr, Gennadi Tymoshenko, and Olexandr Gravets) "The Ukrainian Petrol Corporation", a company that supplied the agriculture industry of Dnipropetrovsk with fuel from 1991 to 1995. Tymoshenko worked as a general director. In 1995, this company was reorganized into United Energy Systems of Ukraine. Tymoshenko served as the president of United Energy Systems of Ukraine, a privately owned middleman company that became the main importer of Russian natural gas to Ukraine, from 1995 to 1 January 1997. During that time she was nicknamed the "gas princess". She was also accused of "having given Pavlo Lazarenko kickbacks in exchange for her company's stranglehold on the country's gas supplies", although Judge Martin Jenkins of the United States District Court for the Northern District of California, on 7 May 2004, dismissed the allegations of money laundering and conspiracy regarding UESU, Somoli Ent. et al....

Question: When did he serve as the president?
1995 to 1 January 1997