#include<stdio.h>
#define pi 3.141592653589
struct area 
{
    float area;
    float radius;
};
int main()
{
    struct area a;
    scanf("%f",&a.radius);
    if(radius<0)
    {
        printf("Invalid input");
        return 0;
    }
    a.area = (a.radius*a.radius)*pi;
    printf("%f",a.area);
    return 0;
}