dic1 = {"A": 4.0, "B": 3.0, "C": 2.0, "D": 1.0, "F": 0}
list1 = []
list2 = []

while True:
    grade = input()

    if grade == "False":
        break
    else:
        score = eval(input())
        list1.append(dic1[grade] * score)
        list2.append(score)

print(f"{sum(list1) / sum(list2):.2f}")