x = int( input() )
if x <= 10:
    y = 2.5
else:
    y = 2.5 +(x - 10) * 1.5

print('%.2f' % y)



/**************************************************************
	Problem: 1043
	User: admin
	Language: Python
	Result: Accepted
	Time:180 ms
	Memory:34244 kb
****************************************************************/