import sys
sys.setrecursionlimit(10**6)
import pypyjit
pypyjit.set_param('max_unroll_recursion=-1')

class Eratosthenes:
    def __init__(self, n):
        self.isPrime = [True]*(n+1)
        self.minfactor = [-1]*(n+1)
        self.isPrime[0], self.isPrime[1] = False, False
        self.minfactor[1] = 1
        for i in range(2, n+1):
            if self.isPrime[i]:
                self.minfactor[i] = i
                for j in range(i*2, n+1, i):
                    self.isPrime[j] = False
                    if self.minfactor[j] == -1:
                        self.minfactor[j] = i
    
    def factorize(self, n):
        factor = []
        while n > 1:
            p = self.minfactor[n]
            cnt = 0
            while self.minfactor[n] == p:
                n //= p
                cnt += 1
            factor.append((p, cnt))
        return factor
    
    def divisor(self, n):
        ans = [1]
        pf = self.factorize(n)
        for p, c in pf:
            L = len(ans)
            for i in range(L):
                v = 1
                for _ in range(c):
                    v *= p
                    ans.append(ans[i]*v)
        return sorted(ans)

def factorization2(n):
    arr = []
    temp = n
    for i in range(2, int(-(-n**0.5//1))+1):
        if temp%i == 0:
            cnt = 0
            while temp%i == 0:
                cnt += 1
                temp //= i
            arr.append([i, cnt])
    if temp != 1:
        arr.append([temp, 1])
    if arr == []:
        arr.append([n, 1])
    return arr

def Euler(n):
    if n > 10**6:
        fact = factorization2(n)
    else:
        fact = E.factorize(n)
    ans = n
    for n, c in fact:
        ans *= 1-(1/n)
    return ans

def divisor2(n):
    ans = []
    for i in range(1, int(n**0.5)+1):
        if n % i == 0:
            ans.append(i)
            if i*i != n:
                ans.append(n//i)
    return sorted(ans)

N = int(input())

def dfs(n):
    if n in D:
        return D[n]
    if n > 10**6:
        div = divisor2(n)
    else:
        div = E.divisor(n)
    cnt = [0]*(len(div)-2)
    for i in range(len(div)-2):
        cnt[i] = Euler(n//div[i+1])
    SUM = 0
    for i in range(len(cnt)):
        SUM += dfs(div[i+1])*(cnt[i]/(n-1))
    D[n] = SUM+n/(n-1)
    return D[n]

E = Eratosthenes(min(10**6, N))
D = dict()

print(dfs(N))