#include<stdio.h>
#define PI 3.141592653589793
int main()
{
    float radious, area;
    scanf("%f", &radious);
    if(radius < 0)
    {
        printf("Invalid input");
        return 0;
    }
    area = PI * radious * radious;
    printf("%.2f", area);
    return 0;
}