K = int(input())

DP = [[0] * (K + 6) for _ in range(K + 1)]
DP[0][0] = 1

for i in range(K):
    for j in range(K):
        if DP[i][j] == 0:
            continue
        # 一段↓の +1 ~ +6 のマスに降らせる
        for k in range(1, 7):
            DP[i + 1][j + k] += DP[i][j]/6

ans = 0
for i in range(1, K + 1):
    ans += i * sum(DP[i][K:])
print(ans)