#pragma ide diagnostic ignored "misc-no-recursion"

#include "bits/stdc++.h"

using namespace std;
typedef long long ll;
typedef long double ldb;

#define TESTCASE 0

static constexpr int MOD = 998'244'353;
static constexpr int INF = 1e9;
static constexpr ldb EPS = 1e-15;

static ll count(ldb r) {
    ll x = r;
    ll res = 0;
    for (ll y = 1; y < r; y++) {
        while (x > 0 && (x * x + y * y) > r * r) {
            x--;
        }
        res += x;
    }
    return res * 4;
}

static void solve([[maybe_unused]] int tc) {
    ll S;
    cin >> S;

    ldb l = 0, r = 1e5;
    while ((r - l) > EPS) {
        ldb m = (l + r) / 2;
        if (count(m) <= S) {
            l = m;
        } else {
            r = m;
        }
    }

    cout << setprecision(10) << fixed << r << endl;
}

int main() {
    ios::sync_with_stdio(false);

    if (const char *f = getenv("REDIRECT_STDOUT"); f) {
        freopen(f, "w", stdout);
    }

    int T = 1;
#if TESTCASE
    cin >> T;
#endif

    for (int t = 1; t <= T; t++) {
        solve(t);
    }

    return 0;
}