#include<iostream> #include<cstdio> 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)*2; else y=x/2-1.5; printf("%.3lf\n",y); return 0; }