


//#pragma GCC optimize("Ofast")
//#pragma GCC target("avx,avx2,fma")
//#pragma GCC optimization ("unroll-loops")

#include<bits/stdc++.h>
#include<string.h>
using namespace std;
#define pb          push_back
#define all(v)      v.begin(),v.end()
#define ya          cout<<"Yes"<<endl;
#define no          cout<<"No"<<endl;
#define ff          first
#define sc          second
#define inf         999999999
#define pi          3.14159265359
#define printv(v)   for(auto x:v)cout<<x<<' ';cout<<endl;
#define takev(v)    for(auto &x:v)cin>>x;
inline  int         random(int a=1,int b=10)
{
    return a+rand()%(b-a+1);
}
typedef long long ll;
inline ll           lcm(ll a,ll b)
{
    return (a*b)/__gcd(a,b);
}
//#define see(x)  cout<<endl<<#x<<" : "<<(x)<<endl;
#define see(args...) \
{ \
    string _s = #args; replace(_s.begin(), _s.end(), ',', ' ');\
    stringstream _ss(_s); istream_iterator<string> _it(_ss); err(_it, args);\
}
void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args)
{
    cerr<< *it << " = " << a <<",\n"[++it==istream_iterator<string>()];
    err(it, args...);
}
#define scc(n) scanf("%lld",&n);
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
const int N=3e6+9,mod=998244353;
ll a[N];
int main()
{
//    ios::sync_with_stdio(0);
//    cin.tie(NULL);
//    cout.tie(NULL);

    for(int i=1;i<=2e5;i++)
    {
        for(int j=1;j<=2e5;j++)
        {
            if(i*j>2e5)break;
            for(int k=1;k<=2e5;k++)
            {
                if(i*j*k>2e5)break;
                a[i*j*k]++;
            }
        }
    }

    for(int i=1;i<=2e5;i++)a[i]+=a[i-1];
    int p;
    cin>>p;
    cout<<a[p]<<endl;

    return 0;
}


#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define mydeb(fmt, ...) fprintf(stderr, fmt, __VA_ARGS__)
//#define mydeb(fmt, ...) 

int main()
{
	int n;
	cin >> n;

	double sum=0;

	for (int i=n-1;i>0;--i)
	{
		sum+=(double)1/i;
	}
	cout << setprecision(16) << sum*n << endl;
}





