// editor5
#include<stdio.h>
#define PI 3.14159
struct circle{
    struct Data{
        float radius;
        
    }d;
};
union Result{
    float radius;
    float area;
};
    

int main()
{
    struct Cricle c;
    union Result r;
    scanf("%f",&c.d.radius);
    if(c.d.radius<0)
    {
        printf("Invalid input");
        return 0;
    }
    r.radius=c.d.radius;
    r.area=PI*r.radius*r.radius;
    printf("%.2f",r.area);
    return 0;
}