#include <cmath>
#include <iostream>
#include <iomanip>

using namespace std;

int main(){
  int n;
  while(cin >> n){
    if ((n == 1) || (n == 3)){
      double area = 1.0*sqrt(3.0)/2.0/2.0;
      cout << area << endl;
    }else{
      double min = 360.0;
      for (int i = 0; i < n; i++){
        double angle1 = 360.0 * (double)i / (double)n;
        double angle2 = angle1 + 120.0;
        if (angle2 >= 360.0)
          angle2 -= 360.0;
        double angle3 = angle1 + 240.0;
        if (angle3 >= 360.0)
          angle3 -= 360.0;

        if ((angle1 > 0) && (angle1 < min))
          min = angle1;
        if ((angle2 > 0) && (angle2 < min))
          min = angle2;
        if ((angle3 > 0) && (angle3 < min))
          min = angle3;
      }
      double min_rad = min * M_PI / 180.0;
      double x = (1.0/3.0-1.0/sqrt(3.0)*sin(min_rad)+tan(M_PI/6.0+min_rad)*1.0/sqrt(3.0)*cos(min_rad)) / (1.0/sqrt(3.0)+tan(M_PI/6.0+min_rad));
      double y = -1.0/sqrt(3.0)*x + 1.0/3.0;      
      int size = (n % 3 == 0)?n:n*3;
      double area = 1.0/sqrt(3.0)*y/2.0*size*2.0;
      printf("%.6llf\n", area);
    }
  }

  return 0;
}