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

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

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

int main() {
    int k;
    cin >> k;
    double ans = 0;
    if(k == 0) {
        printf("%.10lf\n", acos(-1)*acos(-1)/6);
        return 0;
    }
    for (int i = 1; i <= k; ++i) {
        ans += 1.0/(k*i);
    }
    printf("%.10lf\n", ans);
    return 0;
}