#include <cstdint>
#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    int64_t pie11 = 314159265359;
    int r;
    cin >> r;
    double square = (pie11 * r * r - 0.0) / 1e11;
    cout << fixed << setprecision(6) << square << endl;
}
// 64 位输出请用 printf("%lld")