#include<stdio.h>
#include<iomanip>
using namespace std;
int main()
{
    double r;
    cin >> r;
    if(r < 0) {
        cout << "Invalid input";
    } else {
        double area = 3.1416 * r * r;
        cout << fixed << setprecision(2) << area;
    }
    return 0;
}