#include <bits/stdc++.h>
using namespace std;
long long n,i,s,dem;
int main()
{
cin>>n;
s=0;
dem=0;
for (i=1; i<=n; i++)
{
if (i%2==1)
{
dem++;
s=s+i;
}
}
cout<<fixed<<setprecision(2)<<(s*1.0)/(dem*1.0);
return 0;
}
Var i,n:integer;
Begin
Write('nhap n = ');readln(n);
For i:=1 to n do
If i mod 2 = 1 then write(i,' ');
Readln;
End.