Section 4A. Whoever induces a minor to become a prostitute, or who knowingly aids and assists in such inducement, shall be punished by imprisonment in the state prison for not more than five, nor less than three years, and by a fine of five thousand dollars. The sentence of imprisonment imposed under this section shall not be reduced to less than three years, nor suspended, nor shall any person convicted under this section be eligible for probation, parole or furlough or receive any deduction from his sentence for good conduct or otherwise until he shall have served three years of such sentence. Prosecutions commenced under this section shall not be continued without a finding nor placed on file.