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

void main(){
  immutable N = readln().strip().to!int();

  double dp(double c) {
    auto dp = new double[](N+1);
    dp[0] = 0;
    foreach(immutable int i; 1 .. N+1) {
      dp[i] = 1;
      foreach(immutable int j; 0 .. 6)
        dp[i] += ((i-1-j>=0)?dp[i-1-j]:c)/6;
    }
    return dp[N];
  }

  immutable dp_0 = dp(0);

  writeln(dp_0 / (1 - (dp(200) - dp_0) / 200));
}