#define _USE_MATH_DEFINES
#include <stdio.h>
#include <math.h>
int main() {
    
    double r;
    scanf("%lf", &r);
    if (r <= 0) {
        printf("Invalid Input");
        return 1;
    } else {
    
        double area = M_PI * r * r;
        printf("%.2lf", area);
    }
    return 0;
}