#include<cstdio>
#include<ctime>
#include<map>

unsigned int xor128()
{
	static unsigned int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
	unsigned int t = x^(x<<11);
	x = y; y = z; z = w;
	return w=(w^w>>19)^(t^(t>>8));
}

std::map<int, int> m;

int main()
{
	int K;
	scanf( "%d", &K );

	clock_t t = clock();
	int total = 0;
	while( clock() <= t+4*CLOCKS_PER_SEC )
	{
		int sum = 0, cnt = 0;

		for(;;)
		{
			int n = xor128()%6+1;
			sum += n;

			++cnt;

			if( sum == K )
				break;
			if( sum > K )
				sum = 0;
		}

		++m[cnt];
		++total;
	}

	double ans = 0;
	for( auto it = m.begin(); it != m.end(); ++it )
		ans += (double)it->first*it->second/total;

	printf( "%.2f\n", ans );

	return 0;
}