#include<stdio.h>
struct area
{
    float n;
};
int main()
{
    struct area s;
    scanf("%f",&n);
    if(n<=0)
    {
        printf("Invalid input");
    }
    float pi=3.14;
    else
    {
        printf("%.2f",pi*r*r);
    }
    return 0;
}