text: #include <iostream>
  #include <iomanip>
  
  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
          y = x / 2 - 1.5;
  
      cout << fixed << setprecision(3) << y << endl;
  
      return 0;
  }
  