Complex sentence: He has been prime minister of Belgium six times: once from 1949 to 1950, three times from 1958 to 1961 and twice from 1968 to 1973.
Split into simpler sentences: He has been prime minister of Belgium six times. Once from 1949 to 1950, three times from 1958 to 1961 and twice from 1968 to 1973.