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

double solve(int mx) {
  if(mx <= 6) return 1.0/6;
  auto ans = new double[](mx);
  ans.length = mx+2;
  foreach(immutable int x; 1 .. mx+2) {
    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[mx+1] - ans[mx];
}

void main(){
  auto K = readln().strip().to!int();
  double a = solve(K);
  double ans = 0;
  double a_i=1;
  foreach(immutable int i; 1 .. 10000) {
    ans += i * a * a_i;
    a_i *= 1-a;
  }

  writefln("%1.10f", ans+6);
}