签到题，按题意写代码即可

using namespace std;

int main(){
    double x;
    cin>>x;
    double y=0.0;
    if(x>=0&&x<5){
        y=-x+2.5;
    }else if(x>=5&&x<10){
        y=2.0-1.5*(x-3)*(x-3);
    }else{
        y=x/2.0-1.5;
    }
    printf("%.3lf\n",y);
    return 0;
}