#include<stdio.h>
int main()
{
double x;
while(scanf("%lf",&x)!=EOF){
double y;
if(x>=0&&x<2) y=2.5-x;
else if(x>=2&&x<4) y=2-1.5*(x-3)*(x-3);
else if(x>=4&&x<6) y=x/2-1.5;
printf("%.3lf\n",y);
}
return 0;
}
int main()
{
double x;
while(scanf("%lf",&x)!=EOF){
double y;
if(x>=0&&x<2) y=2.5-x;
else if(x>=2&&x<4) y=2-1.5*(x-3)*(x-3);
else if(x>=4&&x<6) y=x/2-1.5;
printf("%.3lf\n",y);
}
return 0;
}