The ventilation of a road tunnel is achieved with the continuous operation of four ventilators. In the control room of the tunnel, there is suitable signaling provided by a PLC so that the responsible operator is informed of the ventilation status according to the following plan: a$.$ When three or four ventilators are in operation, the green traffic light is ON and the cars freely enter the tunnel. b$.$ When only two ventilators are in operation, the yellow traffic light is flashing $($green light is OFF$)$ and the operator has to be on standby to take necessary action. c$.$ When only one ventilator is in operation or all have stopped, the red traffic light is ON and the operator has to intervene by limiting the traffic outside the tunnel. Detection of whether or not ventilators are operating is achieved by four corresponding sensors which are digital inputs to the PLC$.$ After defining the kind of input contacts in relation to ventilators$$ operation and their I$/$O addresses, write the required program that has the minimum number of instructions in any language you wish.