#include <bits/stdc++.h>
#define RREP(i,n,N) for(int i=N-1;i>=(int) n;i--)
#define p(s) cout<<(s)<<endl
using namespace std;

double E[30];
int main() {
	int K;
	cin>>K;
	E[K-1]=1;
	RREP(i,0,K-1){
		E[i]=(E[i+1]+E[i+2]+E[i+3]+E[i+4]+E[i+5]+E[i+6])/6.0+1.0;
	}
	printf("%.3lf",E[0]);
	return 0;
}