I need help with a python program

Develop a function def celsius(f) that converts a temperature from Fahrenheit to Celsius. Here is the formula to go in the reverse direction F=C*1.8+32.

Write a program using your function that asks the user for a temperature, read as a double, and converts it to Celsius. The program should run until the user enters "exit". If the user enters an invalid temperature, ask again.

When the program exits print "Bye."

Here is an example execution trace.

Fahrenheit to Celsius Converter. Enter "Exit" to quit. Enter Temp in Fahrenheit: -58 In Celsius this is -50.0 Enter Temp in Fahrenheit: -40 In Celsius this is -40.0 Enter Temp in Fahrenheit: -22 In Celsius this is -30.0 Enter Temp in Fahrenheit: -4 In Celsius this is -20.0 Enter Temp in Fahrenheit: 14 In Celsius this is -10.0 Enter Temp in Fahrenheit: 15.8 In Celsius this is -9.0 Enter Temp in Fahrenheit: 32 In Celsius this is 0.0 Enter Temp in Fahrenheit: 194 In Celsius this is 90.0 Enter Temp in Fahrenheit: Bad Input Invalid Input. Please try again. Enter Temp in Fahrenheit: Exit Bye.