#include<stdio.h>
#include<math.h>
#define PI 3.1459
int main(){
    double radius;
    double area;
    //const double PI=3.14159265358979323846;
    if(scanf("%lf",&radius);
    if(radius<0){
        printf("Invalid Input");
    }
    else{
        area=PI*radius*radius;
        printf("%2lf\n",area);
        return 0;
    }
}