#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
const int N = 1e6 + 5;
#define int long long
typedef pair<int, int> PII;
#define MAX LONG_LONG_MAX

void solve()
{
    int n;
    cin >> n;
    double l = 1, r = 300000;

    while (l + 1e-6 < r)
    {
        double mid = (l + r) / 2;
        int sum = 0;

        int h = mid;

        for (int i = 1; i <= mid; i++)
        {
            while (i * i + h * h > mid * mid)
                h--;
            if (h == 0)
                break;
            sum += h;
        }
        if (sum * 4 < n)
            l = mid;
        else
            r = mid;
    }
    printf("%.10llf\n", r);
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int tcase;

    solve();
    return 0;
}