#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100005;

int main()
{
    ld x;
    cin >> x;
    ld sm = 0;
    for(int i=1;i<100000005;i++){
        ld ad = 1 / ((x+i)*(x+i));
        sm += ad;
    }
    printf("%.15Lf\n",sm+(1e-8));
    return 0;
}