#include<iostream> #include<iomanip> using namespace std; int main(){ double x,y; cin>>x; if(0<=x&&x<5){ y=-x+2.5; } else if(x<10){ y=2-1.5*(x-3)*(x-3); } else if(x<20){ y=x/2.0-1.5; } cout<<fixed<<setprecision(3)<<y;

return 0; }