Problem: It was decided in IT City to distinguish successes of local IT companies by awards in the form of stars covered with gold from one side. To order the stars it is necessary to estimate order cost that depends on the area of gold-plating. Write a program that can calculate the area of a star.

A "star" figure having n ≥ 5 corners where n is a prime number is constructed the following way. On the circle of radius r n points are selected so that the distances between the adjacent ones are equal. Then every point is connected by a segment with two maximally distant points. All areas bounded by the segments parts are the figure parts.

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Input

The only line of the input contains two integers n (5 ≤ n < 109, n is prime) and r (1 ≤ r ≤ 109) — the number of the star corners and the radius of the circumcircle correspondingly.

Output

Output one number — the star area. The relative error of your answer should not be greater than 10 - 7.

Examples

Input

7 10


Output

108.395919545675

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-7;
struct point {
  long double x, y;
  point(long double x = 0, long double y = 0) : x(x), y(y) {}
  point operator+(const point& b) const { return point(x + b.x, y + b.y); }
  point operator-(const point& b) const { return point(x - b.x, y - b.y); }
  point operator*(double v) const { return point(x * v, y * v); }
  point operator/(double v) const { return point(x / v, y / v); }
  long double inner(const point& b) const { return x * b.x + y * b.y; }
  long double cross(const point& b) const { return x * b.y - y * b.x; }
  point rot(long double angle) const {
    long double cA = cos((long double)angle);
    long double sA = sin((long double)angle);
    return point(x * cA + y * sA, -x * sA + y * cA);
  }
  point rot() const { return point(y, -x); }
};
struct line {
  long double A, B, C;
  line(long double A = 0, long double B = 0, long double C = 0)
      : A(A), B(B), C(C) {}
  line(point a, point b) {
    A = b.y - a.y;
    B = a.x - b.x;
    C = -A * a.x - B * a.y;
  }
  long double subs(const point& b) const { return A * b.x + B * b.y + C; }
  point intersect(const line& b) const {
    long double det = A * b.B - B * b.A;
    long double d1 = C * b.B - B * b.C;
    long double d2 = A * b.C - C * b.A;
    point res = point(-d1, -d2) / det;
    return res;
  }
};
long double angle;
point getP(int k) { return point(1, 0).rot(k * angle); }
int main() {
  int n;
  double r;
  scanf("%d", &n);
  angle = 2 * M_PI / n;
  scanf("%lf", &r);
  long double res = 0;
  int k = n / 2;
  {
    point A = getP(0);
    point B = getP(k);
    point C = getP(-k);
    line l1 = line(A, B);
    line l2 = line(A, C);
    line l3 = line(getP(+1), getP(+1 + k + 1));
    line l4 = line(getP(-1), getP(-1 - k - 1));
    point poly[4] = {A, l1.intersect(l3), point(0, 0), l2.intersect(l4)};
    for (int i = 0; i < 4; i++) {
      point aa = poly[i];
      point bb = poly[(i + 1) % 4];
      res += aa.cross(bb) / 2.0;
    }
  }
  if (res < 0) res = -res;
  printf("%.10lf\n", (double)res * r * r * n);
}