#include <bits/stdc++.h>

using namespace std;
#define IO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ll long long
#define ld long double
const int N = 2e5 + 5, MOD = 998244353;
const ld PI = acos(-1), EPS = 1e-8;
ll s;

bool check(ld r) {
    pair<int, int> p = {floor(r), 1};
    ll total = 0;
    ld rr = r * r;
    while (p.first >= 0) {
        ld d = (ld) p.first * p.first + (ld) p.second * p.second;
        if (rr >= d || d - rr < EPS) {
            total += p.first;
            p.second++;
        } else p.first--;
    }
    total *= 4;
    return (total > s);
}

void doWork() {
    cin >> s;
    ld low = 0.0, high = 1e5, ans;
    while (high - low > EPS) {
        ld mid = (low + high) / 2.0;

        if (check(mid)) ans = mid, high = mid;
        else low = mid;
    }
    cout << fixed << setprecision(10) << ans;
}

int main() {
    IO
    int T = 1;
    //cin >> T;
    while (T--) {
        doWork();
    }
}