Please input expression

x = input("Please input expression:")
lst = x.split(' ')
print(lst)
op = lst[1]
x = int(lst[0])
y = int(lst[2])
while len(lst) >= 3:
    if op in ['+','-','*','/']:
        if op == '+':
            result = x + y
        if op == '-':
            result = x - y
        if op == '*':
            result = x * y
        if op == '/':
    	    result = x / y
        print("The answer is: ",result)
        for i in range(2):
            del lst[0]
            print(lst)
        op = lst[1]
        y = int(lst[2])
        x = result
    else:
	    print("operator error")