from sys import setrecursionlimit
setrecursionlimit(10**6)
def dfs(C, x):
    if x > N:
        return 0.0
    L = list(C)
    M = len(L)
    ret = 0
    for i in range(M+1):
        if i == 0 or i == M:
            ret += 1.0
        else:
            ret += L[i-1] * L[i]
        ret += dfs(L[:i]+[x]+L[i:], x+1)
    ret /= M + 1
    return ret

N = int(input())
C = []
print(dfs(C, 1))