#include <stdio.h>
#include <math.h>
int main(){
    double radius;
    scanf("%f", &radius);
    if (radius<0 || radius>50){
        printf("Invalid Input\n");
    }else{
        double area = acos(-1) * radius * radius;
        printf("%.2f\n", area);
        
    }
    return 0;
    
}