#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>

#define int ptrdiff_t
#define div lldiv
#define div_t lldiv_t
#define abs(a) ((a)<0?-(a):(a))
#define min(a,b) ((a)<(b)?(a):(b))

int K;
double E[30];
main(void) {
    int x;
    scanf("%td\n", &K);
    for (x = 29; x >= K; x--) 
        E[x] = 0.0;
    for (; x >= 0; x--) {
        int i;
        E[x] = 6.0;
        for (i = 1; i <= 6; i++)
            E[x] += E[x+i];
        E[x] /= 6.0;
    }
    printf("%lf\n",E[0]);
    return 0;
}