var a:longint;
    b:real;
begin
read(a);
if a=1 then b:=a*5
else if (a>=2) and (a<=5) then b:=a*4.5
else if (a>=6) and (a<=10) then b:=a*4
else if (a>=10) then b:=a*3.5;
write(b:0:1);
end.



/**************************************************************
	Problem: 1717
	User: admin
	Language: Pascal
	Result: Wrong Answer
****************************************************************/