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

#include <iostream>
#include <iomanip>
using namespace std;
 
float f(float x)
{
    if (x < 5)
        return -x+2.5;
    else if (x < 10)
        return 2-1.5*(x-3)*(x-3);
    if (x < 20)
        return x/2-1.5;
}
 
int main()
{
    float x;
    cin >> x;
    if (x < 0 || x >= 20)
        cout << "输入错误." << endl;
    else
        cout << setprecision(3)<< std::fixed <<  f(x) << endl;
    return 0;
}