def Operation(x):
    global K
    DP = [0] * (K+1)
    for i in range(1,K+1):
        for Dice in range(1,7):
            if i - Dice < 0:
                DP[i] += x
            else:
                DP[i] += DP[i-Dice]
        DP[i] = DP[i] / 6.0 + 1
    return DP[K]

K = int(input())
ng = 0
ok = 1e10
while ok - ng > 1e-3:
    x = (ok + ng) / 2
    if Operation(x) >= x:
        ng = x
    else:
        ok = x
print(ok)