import string

def Add (N1,N2):
    return float(N1) + float(N2)
    
def Subtract (N1,N2):
    return float(N1) - float(N2)
    
def Multiply (N1,N2):
    try:
        Result = float(N1) * float(N2)
    except:
        print "Multiplication overflow"
        Result = 0.0
    return Result
    
def Divide1 (N1,N2):
    if (N2 == 0):
        print "Divide by Zero error"
        Result = 0.0
    else:
        Result = float(N1) / float(N2)
    return Result
    
def Divide (N1,N2):
    try:
        Result = float(N1) / float(N2)
    except:
        print "Divide by Zero error"
        Result = 0.0
    return Result
    
def SquareRoot (N):
    try:
        Result = math.sqrt(N)
    except:
        print "Square root error"
        Result = 0.0
    return Result
    
def Main():
    Accumulator = 0.0
    MoreToDo = True
    while MoreToDo:
        Command = raw_input(str(Accumulator) + " Enter a command --- ")
        Command = string.lower(Command)
        if   (Command == "quit"):       MoreToDo    = False
        elif (Command == "add")      or (Command == "+"): Accumulator = Add(Accumulator, input("Enter new number --- "))
        elif (Command == "subtract") or (Command == "-"): Accumulator = Subtract(Accumulator, input("Enter new number --- "))
        elif (Command == "multiply") or (Command == "*"): Accumulator = Multiply(Accumulator, input("Enter new number --- "))
        elif (Command == "divide")   or (Command == "/"): Accumulator = Divide(Accumulator, input("Enter new number --- "))
        elif (Command == "clear"):      Accumulator = 0.0
        elif (Command == "negate"):     Accumulator = -Accumulator
        elif (Command == "squareroot"): Accumulator = SquareRoot(Accumulator)
        else: print "Illegal Command"
    return