import std.stdio, std.conv, std.math, std.string, std.range, std.array,
       std.algorithm;

enum double[] ans = mkans(21);

double[] mkans(int mx) {
  double[] ans;
  ans.length = mx;
  foreach(immutable int x; 1 .. mx) {
    if (x == 1) ans[x] = 1;
    else {
      double res = 0;
      foreach(immutable int i; 1 .. 7) {
        res += 1.0/6 * ((x-i>0)?ans[x-i]:0);
      }
      ans[x] = res + 1;
    }
  }
  return ans;
}

void main(){
  auto x = readln().strip().to!int();

  writefln("%1.10f", ans[x]);
}