#include<iostream> using namespace std; int main(){ double x,y; cin>>x; if(0<=x<5){ y = -x + 2.5; printf("%.3lf",y); } else if(5<=x<10){ y = 2-1.5*(x-3)*2; printf("%.3lf",y); } else{ y = x/2-1.5; printf("%.3lf",y); } return 0; }