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

int main() {
    float r;
    scanf("%f", &r);

    if (r < 0) {
        printf("Invalid input\n");
    } else {
        float area = M_PI * r * r;  // using math.h constant
        printf("%.2f\n", area);     // print with 2 decimal places
    }

    return 0;
}