n = int(input())
if n == 1:
    p = 5
elif 2 <= n <= 5:
    p = 4.5
elif 6 <= n <= 10:
    p = 4
else:
    p=3.5
print("%.1f" % (n*p))

/**************************************************************
	Problem: 1717
	User: admin
	Language: Python
	Result: Accepted
	Time:587 ms
	Memory:34244 kb
****************************************************************/