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