/************************************************
Algorithmen und Problemloesungen mit C++,
http://www.algorithmen-und-problemloesungen.de
Copyright @2006-2007, Doina Logofatu
************************************************/

#include <fstream>

const int NMAX = 500;
using namespace std;

int main(){
  int n, i, j;
  float p[2*NMAX+1][2*NMAX+1];
  ifstream fin("oktoberfest.in");
  ofstream fout("oktoberfest.out");
  p[0][0] = 1;
  p[1][0] = p[1][1] = 0.5;
  for(i=2; i<=2*NMAX-2; i++){
    p[i][0] = p[i][i] = (float)(p[i-1][0]*0.5);
    for(j=1; j<i; j++)
      p[i][j]=(float) (0.5*p[i-1][j]+0.5*p[i-1][j-1]);
  }
  while(fin && !fin.eof()){
    fin  >> n;
    fout.width(3);
    fout <<  n << ":";
    fout.precision(4);
    fout.flags(ios::fixed);
    fout << 1-p[2*n-2][n-1] << endl;
  }  
  return 0;
}