题解 | #牛牛的绩点#

sum_result = 0
sum_sorce = 0
while True:
    str1 = input()
    if str1 == 'A':
        str2 = input()
        result = int(str2) * 4.0
    elif str1 == 'B':
        str2 = input()
        result = int(str2) * 3.0
    elif str1 == 'C':
        str2 = input()
        result = int(str2) * 2.0
    elif str1 == 'D':
        str2 = input()
        result = int(str2) * 1.0
    elif str1 == 'F':
        str2 = input()
        result = int(str2) * 0.0
    elif str1 == 'False':
        break
    else:
        pass
    sum_result += result
    sum_sorce += int(str2)
    
print('%.2f' % (sum_result/sum_sorce))