#include<bits/stdc++.h>
using namespace std;
int main(){
	double x,y;
	cin>>x;
	if(x>=0&&x<5) y=-x+2.5;
	else if(x>=5&&x<10) y=2-1.5*(x-3)*(x-3);
	else if(x>=10&&x<20) y=x/2.0-1.5;
	cout<<fixed<<setprecision(3)<<y;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main(){
	double x,y;
	cin>>x;
	if(x>=0&&x<5) y=-x+2.5;
	else if(x>=5&&x<10) y=2-1.5*(x-3)*(x-3);
	else if(x>=10&&x<20) y=x/2.0-1.5;
	cout<<fixed<<setprecision(3)<<y;
	return 0;
}