#include<iostream> #include<cstdio> using namespace std; int main(){ float x,y; cin >> x; if(x>=0&&x<5) { y = -x+2.5; } if(x>=5&&x<10) { y = 2-1.5*(x-3)*2; } if(x>=10&&x<20) { y = x/2-1.5; } cout<< printf("%.3f\n", y)<<endl; return 0; }