The state of Kampuchea , officially Democratic Kampuchea , existed between 1975 and 1979 in present-day Cambodia. The state was controlled by the Khmer Rouge  and was founded when KR forces defeated the Khmer Republic of Lon Nol in 1975. Between 1975 and 1979, the state and its ruling Khmer Rouge regime was responsible for the deaths of millions of Cambodians through forced labour and genocide. The KR lost control of most Cambodian territory to Vietnamese occupation. From 1979 to 1982 Democratic Kampuchea survived as a rump state supported by China. In June 1982, the Khmer Rouge formed the Coalition Government of Democratic Kampuchea with two non-communist guerilla factions, which retained international recognition. The state was renamed Cambodia in 1990 in the run up to the UN-sponsored Paris Peace Agreement conference of 1991.
Question: How many years was the time period when millions of Cambodians were killed through forced labord and genocide?
Answer: 4