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