题解 | #牛牛的绩点#

weight_table = {
    'A': 4,
    'B': 3,
    'C': 2,
    'D': 1,
    'F': 0,
}

weighted_score = 0
raw_score = 0

# the interesting part of this Question is to take 2 input one by one.
while True:
    weight = input()
    if weight == 'False':
        break
    else:
        score = int(input())
        weighted_score += weight_table[weight] * score
        raw_score += score

res = '{:.2f}'.format(weighted_score/raw_score)
print(res)