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