#include
int main(void)
{
double x;
scanf("%lf",&x);
if(x {
printf("y = 0\n");
}
else if(x >= 0.0 && x {
printf("y = %lf\n",x);
}
else if(x >= 10.0 && x {
printf("y = 10\n");
}
else if(x >= 20.0 && x {
printf("y = %lf\n",-x/2+20.0);
}
}