# s = input().split() # s = list(map(int, s)) s = int(input()) _print = print def print(num): _print("{:.1f}".format(num)) if s <= 2: print(6) else: if 2 <= s < 10: print((s - 2) * 1.8 + 6) else: print((s - 2) * 1.8 + 6 + ((s - 10) * 1.8) * 0.5)