#include <iostream>
using namespace std;
 
bool done[30];
double dp[30];
 
double solve(int K){
	if(K <= 0)return 0;
	if(done[K])return dp[K];
 
	double res = 1;
	for(int i=1;i<=6;i++)res += solve(K - i) / 6;
 
	done[K] = true;
	return dp[K] = res;
}
 
int main() {
	int K;
	cin >> K;
 
	printf("%.12f\n", solve(K));
	return 0;
}