#include<stdio.h>
#define PI 3.141592653589793
struct area 
{
    float value;
    float area;
}
void main()
{
    struct area a1;
    scanf("%f",&a1.value);
    if(a1.value<=0)
    {
        printf("Invalid input");
    }
    a1.area=PI*a1.value*a1.value;
    printf("%.2f",a1.area);
}