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 int inf = 0x3f3f3f3f, mod = 1000000007;
const double eps = 1e-10, pi = acos(-1.0);
namespace geometry {
struct point {
  double x, y;
  point(double a = 0, double b = 0) : x(a), y(b) {}
};
int fcmp(double val) {
  if (abs(val) < eps)
    return 0;
  else
    return val > 0 ? 1 : -1;
}
point operator+(const point &A, const point &B) {
  return point(A.x + B.x, A.y + B.y);
}
point operator-(const point &A, const point &B) {
  return point(A.x - B.x, A.y - B.y);
}
point operator*(const point &A, const double &p) {
  return point(A.x * p, A.y * p);
}
point operator/(const point &A, const double &p) {
  return point(A.x / p, A.y / p);
}
bool operator==(const point &A, const point &B) {
  return !fcmp(A.x - B.x) && !fcmp(A.y - B.y);
}
bool operator<(const point &A, const point &B) {
  return fcmp(A.x - B.x) < 0 || (!fcmp(A.x - B.x) && fcmp(A.y - B.y) < 0);
}
double dot(point A, point B) { return A.x * B.x + A.y * B.y; }
double cross(point A, point B) { return A.x * B.y - A.y * B.x; }
double length(point A) { return sqrt(dot(A, A)); }
double angle(point A, point B) {
  return acos(dot(A, B) / length(A) / length(B));
}
double dis(point A, point B) {
  return sqrt((A.x - B.x) * (A.x - B.x) + (A.y - B.y) * (A.y - B.y));
}
point rotate(point A, double rad) {
  return point(A.x * cos(rad) - A.y * sin(rad),
               A.x * sin(rad) + A.y * cos(rad));
}
point VectorLineIntersection(point P, point v, point Q, point w) {
  point u = P - Q;
  double t = cross(w, u) / cross(v, w);
  return P + v * t;
}
}  // namespace geometry
using namespace geometry;
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  for (; ch < '0' || ch > '9'; ch = getchar())
    if (ch == '-') f = -1;
  for (; ch >= '0' && ch <= '9'; ch = getchar())
    x = (x << 1) + (x << 3) + ch - '0';
  return x * f;
}
int main() {
  double n, r;
  scanf("%lf%lf", &n, &r);
  point A, B, C, D, E;
  B.x = r;
  C = rotate(B - A, pi / n);
  D = rotate(A - B, -pi / 2 / n);
  E = VectorLineIntersection(A, C, B, D);
  double S = cross(B - A, E - A);
  printf("%.10f", S * n);
  return 0;
}