Roman numerals to Arabic numerals

The program will receive a number in Roman numerals, such as CLI, which is 151 in Arabic numerals. 

Roman numerals use the above table to resemble to given numbers. If a smaller number is in front of a bigger number, it means to minus the small number from the bigger number. For example: 

IV = 4, IX = 9

So all I needed to do was separate each letter and assign them their values, then added it to a list. Then, I just need to check if the value in position i was less then the position in i+1, which if it was, I just add the value of i+1 minus the value of i to the overall counter, and if it wasn't, I just add the value i to the overall counter:

def roman_to_decimal():
    roman = input("Enter your roman numeral: ")
    roman_list = []
    for x in range(0, len(roman)):
        if roman[x] == "I":
            roman_list.append(1)
        elif roman[x] == "V":
            roman_list.append(5)
        elif roman[x] == "X":
            roman_list.append(10)
        elif roman[x] == "L":
            roman_list.append(50)
        elif roman[x] == "C":
            roman_list.append(100)
        elif roman[x] == "D":
            roman_list.append(500)
        elif roman[x] == "M":
            roman_list.append(1000)
    roman_list.append(0)
    decimal = 0
    i = 0
    while i < len(roman_list)-1:
        if roman_list[i] < roman_list[i+1]:
            decimal += roman_list[i+1] - roman_list[i]
            i += 2
        else:
            decimal += roman_list[i]
            i += 1
    print(decimal)