Liters in a cylinder

I still need to make a UI, so below the code in front (it works very well on my laptop)

"""Calculate number of liters in cylinder"""

def litersincylinder():
    pi = 3.141592653589793
    radius = 0
    height = 0
    while radius == 0:
        radius = input("radius in cm.? ")
        if radius.isnumeric() == False:
            if radius == ("q"):
                from sys import exit
                exit()
            else:
                radius = 0
                print ("Only numeric values\n")
    while height == 0:
        height = input("height in cm.? ")
        if height.isnumeric() == False:
            if height == ("q"):
                from sys import exit
                exit()
            else:
                height = 0
                print ("Only numeric values\n")
    liters = round((((pi*(int(radius))*int(radius))*int(height))/1000), 2)
    print ("\n\nNumber of liters: ", liters)
    print ("\n")

go_on = ("q")
go_on = input("Any character to continue or \"q\" to quit: ")
print ("\n")
while go_on != ("q"):
    if go_on != ("q"):
        litersincylinder()
    else:
        from sys import exit
        exit()