gl = {"A":4.0, "B":3.0, "C":2.0, "D":1.0, "F":0} al = [] bl = [] while True: g = input() if g == "False": break else: sco = int(input()) al.append(gl[g]*sco) bl.append(sco) print("%.2f" % (sum(al) / sum(bl)))