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