#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 7;
const int MOD = 1e9 + 7;
const int moveX[] = {-1, 0, 1, 0};
const int moveY[] = {0, 1, 0, -1};
const int INFI = 0x3f3f3f3f;
const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
const double PI = acos(-1);
int main() {
  double n, r, alpha, Sin, Cos, Ctg, ans;
  cin >> n >> r;
  alpha = 180.0 / n;
  Sin = sin(alpha * PI / 180.0);
  Cos = cos(alpha * PI / 180.0);
  Ctg = 1 / tan(3.0 / 2.0 * alpha * PI / 180.0);
  ans = n * r * r * (Sin * Cos - Sin * Sin * Ctg);
  printf("%.7lf", ans);
}
