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