include

include

using namespace std; int main(void){

//freopen("1128.in","r",stdin);
//freopen("1128.out","w",stdout);
int x;
double y;
scanf("%d",&x);
if(x<=15){
	y=4*(double)x/3;
}else{
	y=2.5*(double)x-10.5;
}
printf("%.2lf",y);
return 0;

}