#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <sys/time.h>
using namespace std;
int main()
{
    int K;
    while (cin>>K) {
        timeval tv;
        gettimeofday(&tv, 0);
        double res=0;
        int cnt=0;
        while (true) {
            int c=0, k=0;
            while (k!=K) {
                k+=rand()%6+1;
                if (k>K) k=0;
                ++c;
            }
            res+=c;
            ++cnt;
            if (cnt%100==0) {
                timeval tv2; gettimeofday(&tv2, 0);
                if ((tv2.tv_sec-tv.tv_sec)*1e6+tv2.tv_usec-tv.tv_usec>4e6) break;
            }
        }
        printf("%.3f\n", res/cnt);
    }
}