K=int(raw_input())
exp = [0.0 for i in range(K+1)]
for w in xrange(10000):
    for k in xrange(K-1,-1,-1):
        n=1.0
        for i in xrange(1,7):
            p = k+i
            if p > K:
                p = 0
            n+=exp[p]/6
        exp[k]=n
print exp[0]