K=int(raw_input())
p=[[0]*(K+1) for _ in xrange(K+1)]
p[0][0]=1
for i in xrange(K):
  for j in xrange(K):
    for k in xrange(1,7):
      p[i+1][min(j+k,K)] += p[i][j]
ans=0.0
for i in xrange(1,K+1):
  ans+=float(i*p[i][K])/float(6**i)
print ans