#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:167772160000")
using namespace std;
long double subtcos(long double a) { return 2 * sin(a / 2) * sin(a / 2); }
long double calc(long double a, int n) {
  long double angle = 2 * 3.1415926535897932384626433 / n;
  long double l = sqrt(a * a / 2 / subtcos(angle));
  long double area = n * l * l * sin(angle) / 2;
  long double h = sqrt(a * a - l * l);
  return area;
}
int main() {
  int n;
  cin >> n;
  long double r;
  cin >> r;
  long double angle2 = 3.1415926535897932384626433 -
                       2 * (3.1415926535897932384626433 * (n / 2 - 1)) / n;
  long double dist1 =
      r * sqrt(2 * subtcos(2 * 3.1415926535897932384626433 / n));
  long double test = 2 * 3.1415926535897932384626433 / n;
  long double aaa = cos(test);
  long double ffff = subtcos(test);
  long double dist2 = dist1 * sqrt(1.0 / 2 / subtcos(angle2));
  long double gggg = 1.0 / 2 / subtcos(angle2);
  long double angle3 = 3.1415926535897932384626433 / n;
  long double area1 = dist2 * dist2 * sin(angle3) / 2;
  area1 *= n;
  long double dist3 = sqrt(2 * dist2 * dist2 * subtcos(angle3));
  long double area2 = calc(dist3, n);
  cout << fixed << setprecision(20) << area1 + area2;
  return 0;
}
