import sequtils,strutils
var
    P : array[201,float64]
    K = stdin.readline.parseInt
    ans : float64
    a,b : int
P[0] = 1
for i in 1..5000:
    var P2 : array[201,float64]
    for j,p in P[0..<K]:
        for k in 1..6:
            if j + k == K:
                ans += i.float64 * p / 6
            elif j + k < K:
                P2[j + k] += p / 6
            else:
                P2[0] += p / 6
    P = P2
echo ans