#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){
	double x;
	cin>>x;
	double y;
	if(0<=x&&x<5){
		y=-x+2.5;
	}
	else if(5<=x&&x<10){
		y=2-1.5*(x-3)*(x-3);
	}
	else{
		y=x/2-1.5;
	}
	cout<<fixed<<setprecision(3)<<y;
	return 0;
}