#include <iostream>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>
#include <limits>


static const int MOD = 1000000007;
using ll = long long;
using u32 = uint32_t;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n;
    cin >> n;
    double ans = 1;
    for (int i = 1; i < n; ++i) {
        ans += (3*i*i-i-2)/12.0+2.0/(i+1);
    }
    printf("%.10lf\n", ans);
    return 0;
}