from sys import stdin
read1 = stdin.read().split()

s = 0
n = 0
dict1 = {"A":4,"B":3,"C":2,"D":1,"F":0}
for i in range(len(read1)//2):
    s += dict1[read1[2*i]]*int(read1[2*i+1])
    n += int(read1[2*i+1])
print(f"{s/n:.2f}")