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