#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef set<int> si;
const int inf = 1e9;
const int mod = 1e9+7;

main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  double x;
  cin >> x;
  double s = 0.0;
  FOR(i, 1, 10000000){
    s += (1.0 / ((x+i)*(x+i)));
    //cout << s << endl;
  }
  s += 1.0 / (x + 10000000);
  printf("%13.11f\n", s);
}