#include <bits/stdc++.h>
using namespace std;

double E[ 30 ];

int main()
{
int i;
int j;
int K;

	cin >> K;

	for( i = K - 1; i >= 0; i-- )
	{
		for( j = 1; j <= 6; j++ ) E[ i ] += E[ i + j ];

		E[ i ] /= 6;
		E[ i ] += 1;
	}

	cout << E[ 0 ] << endl;

	return 0;
}