Bonilla Company's office building was destroyed by a tornado. The insurance company paid Bonilla $600,000 for the destruction of the office building within 30 days after the tornado. At the time of the tornado, Bonilla had an adjusted basis of $240,000 in the office building. Within six months after the tornado, Bonilla bought a new office building for $500,000 by paying $320,000 in cash and signing a mortgage note for $180,000. What is the minimum amount of gain that Bonilla must recognize on the involuntary conversion of its office building?