# include<iostream> using namespace std; int main(){ double x; cin >> x; if(x<5){ printf("%.3lf",-1*x+2.5); }else if(x<10){ printf("%.3lf",2-1.5*(x-3)*2); }else if(10<=x<20){ printf("%.3lf",1*x-1.5); } return 0; }