import sys
a = []
data_flag = 0
score = 0
timer = 0
score_tycle = {"A" :4.0,"B": 3.0,"C": 2.0,"D": 1.0,"F": 0}
for line in sys.stdin:
a +=line.split()
for x in a:
if x == "False":
break
else:
if data_flag == 0:
if x in score_tycle:
tem = float(score_tycle[x])
data_flag = 1
else:
try:
data_flag = 0
tem = tem*float(x)
timer =float(x) + timer
score = tem+score
except ValueError:
continue
print("%0.2f"%(score/timer))

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