import sys
sys.setrecursionlimit(10**6)

E = dict()
E[0] = 0.0
E[1] = 1.0
def rec(x):
    if E.get(x, None) is not None:
        return E[x]
    res = 0.0
    for i in range(x):
        res += (rec(i) + rec(x - i - 1)) / (x - 1)
    E[x] = res
    return res

n = int(input())
print(rec(n))