#include<stdio.h>
#include<math.h>
int main() {
    float radius,area
    scanf("%f", &radius);
    if (radius < 0) {
        printf("Invalid Input\n");
    } else {
        float area = 3.1415 * pow(radius, 2);
        printf("%.2f\n", area);
    }
    return 0;
}