def calculate(operator, nr1, nr2):
    if operator != "/" or operator != "-" or operator != "+" or operator != "*":
        return "Invalid Operator!"
    elif operator == "/":
        try:
            return str(nr1//nr2)
        except:
            return "Error!"
    elif operator == "-":
        try:
            return str(nr1-nr2)
        except:
            return "Error!"
    elif operator == "+":
        try:
            return str(nr1+nr2)
        except:
            return "Error!"
    elif operator == "*":
        try:
            return str(nr1*nr2)
        except:
            return "Error!"