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