#include <stdio.h>
#include <math.h>

int main() {
    double radius;
    double area;
    scanf("%lf", &radius);
    
    if(radius >= 0 && radius <= 50) {
        area = M_PI * radius * radius;
        printf("%.2f\n", area);
    } else {
        printf("Invalid Input\n");
    }
    
    return 0;