import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
#sys.setrecursionlimit(1000000)
#import math
import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
from collections import defaultdict
#from collections import deque
#import copy #DeepCopy: hoge = [_[:] for _ in hogehoge]
from functools import lru_cache
#@lru_cache(maxsize=None)
#MOD = pow(10,9) + 7
MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]


def main():
    N = int(input())
    @lru_cache(maxsize=None)
    def solve(x):
        if x == 1:
            return 1
        ret = 0
        for i in range(x):
            print(i,x-1-i)
            ret += (solve(i) + solve(x-1-i))/(x-1)
        return ret
    print(solve(N))
        
        


if __name__ == '__main__':
    main()