#inclue<stdio.h>
#include<math.h>
int main()
{
    double radius, area;
    scanf("%1f", &radius);
    if (radius < 0)
    {
        printf("Invalid input\n");
    }
    else
    {
        area = M_PI * radius * radius;
        printf("%.2flf\n", area);
    }
    return 0;
}