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 long long INF = 1 << 28;
const long long LINF = 1ll << 61;
inline long long getnum() {
  register long long r = 0;
  register bool ng = 0;
  register char c;
  c = getchar();
  while (c != '-' && (c < '0' || c > '9')) c = getchar();
  if (c == '-') ng = 1, c = getchar();
  while (c != ' ' && c != '\n') r = r * 10 + c - '0', c = getchar();
  if (ng) r = -r;
  return r;
}
template <class T>
inline void putnum(T x) {
  if (x < 0) putchar('-'), x = -x;
  register short a[20] = {}, sz = 0;
  while (x > 0) a[sz++] = x % 10, x /= 10;
  if (sz == 0) putchar('0');
  for (int i = sz - 1; i >= 0; i--) putchar('0' + a[i]);
}
inline void putsp() { putchar(' '); }
inline void putendl() { putchar('\n'); }
inline char mygetchar() {
  register char c = getchar();
  while (c == ' ' || c == '\n') c = getchar();
  return c;
}
long long C(int x, int y) {
  long long ans = 1;
  for (int i = 1; i <= y; i++) ans = ans * (x - i + 1) / i;
  return ans;
}
long long kissme(long long x, int y) {
  long long ans = 1;
  while (y > 0) {
    if (y & 1) ans = ans * x;
    x = x * x;
    y >>= 1;
  }
  return ans;
}
struct point {
  long double x, y;
  point(long double _x = 0, long double _y = 0) {
    x = _x;
    y = _y;
  }
  point operator*(point tmp) {
    return point(x * tmp.x - y * tmp.y, x * tmp.y + y * tmp.x);
  }
  point operator+(point tmp) { return point(x + tmp.x, y + tmp.y); }
  point operator-(point tmp) { return point(x - tmp.x, y - tmp.y); }
  point operator*(long double tmp) { return point(x * tmp, y * tmp); }
  point operator/(long double tmp) { return point(x / tmp, y / tmp); }
  long double len() { return x * x + y * y; }
  long double det(point tmp) { return x * tmp.y - y * tmp.x; }
  void out() { cout << fixed << setprecision(10) << x << " " << y << endl; }
};
const long double pi = acos(-1);
point intersection(point p1, point p2, point q1, point q2) {
  return p1 + (p2 - p1) * ((q2 - q1).det(q1 - p1) / (q2 - q1).det(p2 - p1));
}
int n, r;
point unitangle(int x) {
  return point(cos(2 * pi / n * x), sin(2 * pi / n * x)) * r;
}
int main() {
  cin >> n >> r;
  point x;
  x = intersection(unitangle(0), unitangle((n - 1) / 2), unitangle(1),
                   unitangle((n + 1) / 2 + 1));
  cout << fixed << setprecision(12) << point(r, 0).det(x) * n << endl;
  return 0;
}