#include<stdio.h>
#define PI 3.1415926535897

float calculate_area(float radius)
{
    return PI * r * r;
}
void print_area(float area)
{
    printf("%.2f\n",area);
}
int main()
{
    float r;
    scanf("%f",&r);
    if(r<0)
    {
        printf("Invalid input");
        return 1;
    }
    
        float area = calculate_area( radius);
        print_area(area);
        
    
    return 0;
}