Free form back to fixed form fortran

Question

So I wrote some Fortran in the .f90 format and I need the file extension to be .f for compilation reason. Im under the assumption that ive written the fortran in iin the newest fortran 90 way and i need to convert it back to .f fortran 77 way.

  program p1
    implicit none
    integer :: choice
    real :: inputValue 

     do while(choice /= 0) 
            print *, ' '
            print *, 'Enter a conversion option (1-6 or 0 to exit):'
            print *, '-------------'
            print *, '(1) Pounds to Kilograms'
            print *, '(2) Kilograms to Pounds'
            print *, '(3) Feet to meters'
            print *, '(4) Meters to feet'
            print *, '(5) farenheit to Celsius'
            print *, '(6) Celsius to Fahrenheit'
            print *, '(0) Exit this progrm'
            print *, '-------------'
            READ(*,*) choice

            IF (choice == 1) THEN
                print *, 'Please enter the number (Integer) of Pounds to be converted into Kilograms'
                READ(*,*) inputValue
                inputValue  = inputValue / 2.20
                print *, 'Your value is:', inputValue
             ELSE IF (choice == 2) THEN
                print *, 'Please enter the number (Integer) of Kilograms to be converted into Pounds'
                READ(*,*) inputValue
                inputValue = inputValue * 2.20
                print *, 'Your value is:', inputValue
             ELSE IF (choice == 3) THEN
                print *, 'Please enter the number (Integer) of Feet to be converted into Meters'
                READ(*,*) inputValue
                inputValue = inputValue / 3.28
                print *, 'Your value is:', inputValue
             ELSE IF (choice == 4) THEN
                print *, 'Please enter the number (Integer) of Meters to be converted into Feet'
                READ(*,*) inputValue
                inputValue = inputValue * 3.28
                print *, 'Your value is:', inputValue
             ELSE IF (choice == 5) THEN
                print *, 'Please enter the number (Integer) of Fahrenheit to be converted into Celsius'
                READ(*,*) inputValue
                inputValue = (5.0/9.0) * (inputValue - 32)
                print *, 'Your value is:', inputValue
             ELSE IF (choice == 6) THEN
                print *, 'Please enter the number (Integer) of Celsius to be converted into Fahrenheit'
                READ(*,*) inputValue
                inputValue = (inputValue * 9.0/5.0) + 32
                print *, 'Your value is:', inputValue
             ELSE IF (choice == 0) THEN
                print *, 'EXIT'
        
             END IF 
    ENDDO  

  end program p1