#include <bits/stdc++.h>

using namespace std;

string sum(string a,string b)
{
		int carry = 0, n;
		string t;
		int aidx, bidx;
		aidx = a.size() - 1;
		bidx = b.size() - 1;
		while (1)
		{
			if (aidx < 0 && bidx < 0)
			{
				break;
			}
			else if (aidx >= 0 && bidx >= 0)
			{
				n = (a[aidx] - '0') + (b[bidx] - '0');
				n += carry;
				if (n >= 10)
				{
					n -= 10;
					carry = 1;
				}
				else
				{
					carry = 0;
				}
				t = char(n + '0') + t;
				aidx--;
				bidx--;
			}
			else if (aidx >= 0 && bidx < 0)
			{
				n = a[aidx] - '0';
				n += carry;
				if (n >= 10)
				{
					n -= 10;
					carry = 1;
				}
				else
				{
					carry = 0;
				}
				t = char(n + '0') + t;
				aidx--;
			}
			else if (aidx < 0 && bidx >= 0)
			{
				n = b[bidx] - '0';
				n += carry;
				if (n >= 10)
				{
					n -= 10;
					carry = 1;
				}
				else
				{
					carry = 0;
				}
				t = char(n + '0') + t;
				bidx--;
			}
		}
		if (carry == 1)
		{
			t = '1' + t;
		}
		return t;
}

int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

  int N;
  string A = "0";
  string B = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";

  cin >> N;

  for(int i=0;i<N;i++)
  {
    A = sum(A,B);
  }

  if(N<9)
  {
    cout << "0." << A << '\n';
  }
  else
  {
    int x = 1;
    if(N>81) x = 2;
    for(int i=0;i<A.length();i++)
    {
      if(i==x)
      {
        cout << ".";
      }
      cout << A[i];
    }
    cout << '\n';
  }
	return 0;
}