#include<stdio.h>
#include<math.h>
int main(){
    double radius;
    double area;
    const double PI=3.14;
    if(scanf("%1f",&radius)!=1)return 1;
    if(radius<0){
        printf("Invalid Input\n");
    }
    else{
        area=PI*radius*radius;
        printf("%2f\n",area);
        return 0;
    }
}