#include <iostream>
#include <string>
#include <algorithm>
#include <math.h>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <list>
#define ll long long int
#define ull unsigned long long int
#define ld long double
using namespace std;

int main() {
	long double N;
	cin >> N;
	long double ans = 0;

	for (int i = 1; i <= N-1; i++) {
		ans += N / (N - i);
	}
	cout.precision(10);
	cout << ans << endl;
}
#include <bits/stdc++.h>
//#include <atcoder/all>

using namespace std; 

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;
typedef long long LL;
typedef vector<LL> VL;
typedef vector<VL> VVL;
typedef pair<LL, LL> PLL;
typedef vector<PLL> VPLL;
typedef vector<bool> VB;
typedef priority_queue<LL> PQ_DESC;
typedef priority_queue<LL, VL, greater<LL>> PQ_ASC;
typedef priority_queue<PII> PQ_DESC_PII;
typedef priority_queue<PII, vector<PII>, greater<PII>> PQ_ASC_PII;
typedef priority_queue<VL> PQ_DESC_VL;
typedef priority_queue<VL, vector<VL>, greater<VL>> PQ_ASC_VL;
typedef priority_queue<PLL> PQ_DESC_PLL;
typedef priority_queue<PLL, vector<PLL>, greater<PLL>> PQ_ASC_PLL;

#define ALL(c) (c).begin(),(c).end()
#define PB push_back
#define MP make_pair
#define SORT_ASC(c) sort(ALL(c))
//#define SORT_DESC(c) sort(ALL(c), greater<typeof(*((c).begin()))>())
#define SORT_DESC(c) sort((c).rbegin(),(c).rend())
#define REV(c) reverse((c).begin(), (c).end())
#define SIZE(a) LL((a).size())

#define FOR(i,a,b) for(LL i=(a);i<(b);++i)
#define ROF(i,a,b) for(LL i=(b-1);i>=(a);--i)
#define REP(i,n) FOR(i,0,n)
#define PER(i,n) ROF(i,0,n)

const double EPS = 1e-10;
const double PI  = acos(-1.0);
const LL LARGE_INT = 1e9+100;
const LL INF = 2e9+100;
const LL INF_LL = (LL)INF*(LL)INF;
const LL MOD = 1e9+7;

//debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

LL modpow(LL a, LL n) {
    LL res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % MOD;
        a = a * a % MOD;
        n >>= 1;
    }
    return res;
}

const int MAX = 510000;
LL fac[MAX], finv[MAX], inv[MAX];
// テーブルを作る前処理。main()ないでCOMinit()する
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
// 二項係数計算
LL COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

void Main()
{
    LL n;cin>>n;
    double result = 0;

    REP(i,n){
        result += n/(i+1.0);
    }

    cout<<result-1<<endl;


   

    
    
	return;
}

int main()
{
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(15);
	Main();
    return 0;
}