#include <bits/stdc++.h>

using namespace std;
using ld = long double;

int s;
// 
// SSSS

bool inside(ld r, int x, int y) {
    return 1ll * x * x + 1ll * y * y <= r * r;
}
bool check(ld r) {
    int rm = 0;
    int x = r;
    int y = 1;
    while (x > 0) {
        while (x > 0 and not inside(r, x, y))
            --x;
        rm += x;
        ++y;
    }
    return 4 * rm > s;
}

signed main() {
    ios::sync_with_stdio(false); cout.tie(nullptr); cin.tie(nullptr);
    cin >> s;
    ld l = 0, r = 2 * sqrtl(s);
    for (int _ = 0; _ < 100; ++_) {
        ld m = (l + r) / 2;
        if (check(m))
            r = m;
        else l = m;
    }
    cout << fixed << setprecision(12) << l << '\n';
    return 0;
}