python/TangDou/LianXiTi50/39.cpp

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;
    double s = 0;
    if (n % 2 == 0) {
        for (int i = 2; i <= n; i = i + 2)
            s += 1.0 / i;
    } else {
        for (int i = 1; i <= n; i = i + 2)
            s += 1.0 / i;
    }
    cout << s << endl;
    return 0;
}