got_height = False

while not got_height:
    m_str = raw_input("Enter your height (in metres): ")
    try:
        metres = float(m_str)
        got_height = True # if we're here, it was converted.
    except:
        print "Please enter a number."

feet = 39.37 * metres / 12
print "You are " + str(feet) + " feet tall."