#include <bits/stdc++.h>

using namespace std;

double trigamma(double x)
{
  x += 7;
  double p = 1 / x / x;
  p = (((((p * 5 / 66 - 1.0 / 30) * p + 1.0 / 42) * p - 1.0 / 30) * p + 1.0 / 6) * p + 1) / x + p / 2.0;
  for(int i = 0; i < 6; i++) {
    p = 1 / --x / x + p;
  }
  return (p);
}

int main()
{
  double x;
  cin >> x;
  cout << fixed << setprecision(15) << trigamma(x) << endl;
}