// editor5
#include<stdio.h>
union circle{
    double radius;;
    double area;
};
int main()
{
    
  union circle c;
  const double PI=3.14159;
    if(scanf("%lf",&radius)!=1)
    {
        printf("Invalid input");
        return 0;
    }
    if(c.radius<0)
    {
        printf("Invalid input");
        return 0;
    }
    double r=c.radius;
    c.area=PI*r*r;
    printf("%.2f",c.area);
    return 0;
}