#include<cstdio>
#include<algorithm>
#define rep(i,a) for(int i=0;i<(a);++i)

const int MAX_K = 20;

double E[MAX_K+1];
int K;

double rec( int x )
{
	double &ret = E[x];

	if( x >= K )
		return ret=0;

	if( ret >= 0 )
		return ret;

	ret = 1;

	rep( i, 6 )
		ret += rec(x+i+1)/6;

	return ret;
}

int main()
{
	std::fill( E, E+MAX_K+1, -1 );

	scanf( "%d", &K );

	printf( "%.5f\n", rec(0) );

	return 0;
}