A circuit outputs a digit in a the form of 4 bits. 0 is represented by 0000, 1 is represented by 0001,...., 9 by 1001. A combinational circuit is to be designed which takes 4 bits as input and output as 1, if the digit is ≥ 5, and 0 otherwise. If only AND, OR and NOT gates may be used, what is the minimum number of gates required?