#include<string.h>
int main() 
{
    float radius;
    scanf("%f", &radius);
    
    if (radius<0)
    {
        printf("Invalid input");
    }
    else
    {   
        int PI=3.14159;
        float area = PI*radius*radius;
        printf("%.2f\n", area);
    }
    return 0;
}