#include<stdio.h>
#define pi 3.141592653589
struct areacircle{
    int area;
    float pi 3.14;
    float radius;
int main()
{
    struct areacircle ac;
    scaanf("%d", &ar.radius);
    if(radius<0)
    {
        printf("Invalid input");
    }
    ac.area=(ac.radius*ac.radius)*pi;
    printf("%f", ac.area);
    return 0;
}