// editor5
#include <stdio.h>
struct areaofcircle
{
    float r;
    float pi=3.14159265359;
    float area;
};
int main()
{
    struct afc b;
    scanf("%f",&b.r);
    if(b.r<=0 || b.r<=100)
    {
        printf("Invalid input");
        return 0;
    }
    b.area=b.pi*b.r*b.r;
    printf("%.2f",b.area);
    return 0;
}