print("Hi, I am Marvin, your personal bot.")
print("Do you want to add or substract  ?")
command = input("How can I help ?")
if command == "add" or command == "plus":
    print("Let's add 3 numbers.")
    input1 = input("Number 1> ") # input numbers are strings#
    input2 = input("Number 2> ")
    input3 = input("Number 3> ")
    number1 = int(input1) # use int to convert string to integer#
    number2 = int(input2)
    number3 = int(input3)
    result = number1 + number2 + number3  #by using add #
    output = str(result) #result of operation#
    print(input1 + " + " + input2 + " + " + input3 + " = " + output)
elif command == "substract":
    print(" Let's substract some numbers.")
    input1 = input("Number 1> ")
    input2 = input("Number 2> ")
    number1 = int(input1)
    number2 = int(input2)
    result = number1 - number2
    output = str(result)
    print(input1 + " - " + input2+" = " + output)
else:
    print("Sorry, I don't understand")