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

enum double[] ans = mkans(20);

double[] mkans(int mx) {
  double[] ans;
  foreach(immutable int i; 0 .. mx) {
    ans ~= e(i);
  }
  return ans;
}

double e(int x) {
  double res = 0;
  if (x < 1) return 0;
  if (x == 1) return 1;
  foreach(immutable int i; 1 .. 7) {
    res += 1.0/6 * e(x-i);
  }
  ++ res;
  return res;
}

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

  writeln(ans[x]);
}