#include<bits/stdc++.h>
using namespace std;
int main(){
	long long n,l,r,mid;
	scanf("%lld",&n),l=1,r=n;
	while(l<r){
		mid=(l+r+1)>>1;
		if(mid+1<=((n+1)<<1)/mid)l=mid;
		else r=mid-1;
	}printf("%lld\n",n+1-r);
	return 0;
}
#include <bits/stdc++.h>
using namespace std;

#define For(i,a,b) for(int (i) = (a);(i) < (b);i++)
#define Rep(i,n) For((i),0,(n))
#define All(a) (a).begin(),(a).end()
#define sp " "
#define INF 1e18
#define INT_INF 1e9

typedef long long ll;
const ll MOD = 1000000007;
const ll MOD_9 = 998244353;

vector<char> boin = {'a','i','u','e','o'};
vector<char> alphabet = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
vector<char> Capital =  {'Q','W','E','R','T','Y','U','I','O','P','A','S','D','F','G','H','J','K','L','Z','X','C','V','B','N','M'};

int main(){
    int N;
    cin >> N;
    double ans = 0;
    for(int i = 1;i < N;i++){
        ans += (double)1/i;
        //cout << i << sp << E[i] << endl;
    }
    cout << fixed << setprecision(8) <<  N*ans << endl;
    cin >> N;
}