#include <stdio.h>
#include <math.h>
int main()
{
    float r,area,PI;
    PI=3.14;
    scanf("%f",&r);
    if(r>0)
    {
        area=r*r*PI;
    printf("the area of the circle is %f",area);
    }
    else 
    {
        printf("invalid");
    }
    return 0;
}