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 pi = 3.141592653589793;
const double eps = 1e-11;
const int oo = 0x3f3f3f3f;
template <class T>
inline void checkmin(T &a, T b) {
  if (b < a) a = b;
}
template <class T>
inline void checkmax(T &a, T b) {
  if (b > a) a = b;
}
template <class T>
inline T sqr(T x) {
  return x * x;
}
template <class T>
inline T lowbit(T n) {
  return (n ^ (n - 1)) & n;
}
template <class T>
inline int countbit(T n) {
  return (n == 0) ? 0 : (1 + countbit(n & (n - 1)));
}
template <class T>
inline T gcd(T a, T b) {
  T c;
  while (a != 0) {
    c = a;
    a = b % a;
    b = c;
  }
  return b;
}
template <class T>
inline T mabs(T a) {
  if (a < 0)
    return -a;
  else
    return a;
}
typedef vector<int> VI;
typedef vector<VI> VII;
typedef vector<string> VS;
#pragma comment(linker, "/STACK:36777216")
int TEST_TO;
int TEST_FROM;
inline double mine(int n, int r) {
  double alpha = pi / (2.0f * n);
  double gamma = pi / (1.0f * n);
  double beta = pi - (alpha + gamma);
  double a = 1.0f * r;
  double b = (a * sin(gamma)) / (sin(beta));
  double c = (a * sin(alpha)) / (sin(beta));
  double h = sin(alpha) * b;
  double res = n * h * a;
  return res;
}
inline int solve(int testnum) {
  int n, r;
  scanf("%d%d", &n, &r);
  double res = mine(n, r);
  printf("%.20lf\n", res);
  return 0;
}
int main(int argc, char *argv[]) {
  ios::sync_with_stdio(false);
  int t = 1;
  if (argc > 1) t = atoi(argv[1]);
  TEST_FROM = 1;
  TEST_TO = t;
  for (int _t = (1); _t < int(t + 1); _t++) {
    int ret = ::solve(_t);
    if (ret == -1) break;
  }
  return 0;
}