#include <cstdio>
using namespace std;

double A[210], B[210];
int main() {
    int K; scanf("%d", &K);
    for(int i=K+1; i<=K+5; i++) {
        A[i] = 1;
    }
    for(int i=K-1; i>=0; i--) {
        // E[i] = (E[i+1] + E[i+2] + ... E[i+6]) / 6 + 1
        for(int k=1; k<=6; k++) {
            A[i] += A[i+k] / 6.0;
            B[i] += B[i+k] / 6.0;
        }
        B[i]++;
    }

    // E = aE + b -> E = b / (1-a)
    printf("%.12f\n", B[0] / (1.0 - A[0]));
    return 0;
}