#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

ll count(double r) {
    ll res = 0;
    for (int i = 1; i <= r; i++) {
        res += floor(pow(r * r - i * i, 0.5));
    }
    return 4 * res;
}

void solve() {
    ll s;
    cin >> s;
    double lo = 1, hi = 1e5;
    double delta = 1e-7;

    while (lo + delta < hi) {
        double mid = (lo + hi) / 2;
        if (count(mid) <= s) {
            lo = mid + delta;
        } else {
            hi = mid;
        }
    } 
    cout << lo << '\n';
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.precision(16);
    int t = 1;
    //cin >> t;
    while (t--) solve();
    return 0;
}