#include <iostream>
#include<cstdio>
using namespace std;
int n;
int main()
{
  double sum=0;
  int i;
  cin>>n; 
  for(int i=1;i<=n;i++){
  if(i%2==0) sum-=1.0/i;
  else sum+=1.0/i;
  }
  printf("%.4lf\n",sum);
   return 0;
}