7-87 1027 累加和

#include <algorithm>
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <limits>
#include <numeric>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>

using i32 = std::int32_t;
using i64 = std::int64_t;
using u32 = std::uint32_t;
using u64 = std::uint64_t;
using pii = std::pair<i32, i32>;
using pll = std::pair<i64, i64>;
using vi = std::vector<i32>;
using vll = std::vector<i64>;
using vpii = std::vector<pii>;
using vpll = std::vector<pll>;

void solve();

int main()
{
    std::cin.tie(nullptr)->sync_with_stdio(false);
    solve();
}

i32 get_deminator(i32 n)
{
    return 2 * n - 1;
}

double get_frac(i32 n)
{
    return static_cast<double>(1) / get_deminator(n);
}

void solve()
{
    i32 n;
    while (std::cin >> n)
    {
        double sum = 0;
        for (i32 i = 1; i <= n; ++i)
        {
            sum += get_frac(i);
        }
        std::cout << std::fixed << std::setprecision(6) << sum << std::endl;
    }
}