#define _USE_MATH_DEFINES
#include <stdio.h>
#include <math.h>
#define M_PI 3.14159
int main() {
    
    float r;
    scanf("%f", &r);
    if (r <0) {
        printf("Invalid Input");
        return 1;
    } eles {
        
        float area = M_PI * (r * r);
        printf("%.2f", area);
    }
    return 0;
    
}