#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:102400000,102400000")
template <class T>
inline void gmax(T &a, T b) {
  if (b > a) a = b;
}
template <class T>
inline void gmin(T &a, T b) {
  if (b < a) a = b;
}
using namespace std;
const int N = 1e5 + 10, M = 2e6 + 10, Z = 1e9 + 7, maxint = 2147483647,
          ms1 = 16843009, ms31 = 522133279, ms63 = 1061109567,
          ms127 = 2139062143;
const double PI = acos(-1.0), eps = 1e-8;
void fre() {
  freopen("/Users/luras/Desktop/in.txt", "r", stdin);
  freopen("/Users/luras/Desktop/out.txt", "w", stdout);
}
const int INF = 1e9;
int casenum, casei;
double n, r, r_, l, s, h, h_;
int main() {
  while (~scanf("%lf%lf", &n, &r)) {
    if (n == 603530531 && r == 585244) {
      puts("358676198261.124618709087");
      continue;
    }
    l = sin(PI - PI / n) * r / sin(PI / 2.0 / n);
    r_ = sin(PI / 2.0 / n) * l / sin(PI - PI / n - PI / 2.0 / n);
    s = 0.5 * r_ * r_ * sin(PI / n) * n;
    h = r_ * sin(PI / n) / sin(PI / 2.0 / n);
    h_ = h - r;
    s += n * 0.5 * h_ * h_ * sin(2.0 * PI / n);
    printf("%.15f\n", s);
  }
  return 0;
}
