include <bits/stdc++.h>

define ll long long int

define ld long double

using namespace std; int main(){

ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
ll n;
cin>>n;
ld m = 1, k = 1, ans = 0;
for(int i = 0; i<n; i++){
    ans+=(m/k);
    m++;
    k+=2;
}
cout.precision(3);
cout<<fixed<<ans;

} //TECHNOBLADE NEVER DIES