#include <bits/stdc++.h>
using namespace std;

int N;

double dfs( vector< vector< double > > &dp, int x, int t ){
  if( x >= N )
    return 1.0 * t;
  if( dp[ x ][ t ] < 1e9 )
    return dp[ x ][ t ];
  double res = 0;
  for( int i = 1; i <= 6; ++i )
    res += dfs( dp, x + i, t + 1 );
  return dp[ x ][ t ] = res / 6;
}

signed main(){
  cin >> N;
  vector< vector< double > > dp( N + 1, vector< double >( N + 6, 2e9 ) );
  cout << fixed << setprecision( 13 ) << dfs( dp, 0, 0 ) << endl;
  return 0;
}