#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define ALL(v) v.begin(),v.end()
#define dbg(x) cerr << #x << ": " << (x) << endl;
#define sq(x) ((x) * (x))

int main() {
    ll n;
    cin >> n;

    ++n;
    n = (n + 3) / 4;

    auto f = [&](ld mid) {
        ll cnt = 0;
        for (ll i = 1; i <= mid; ++i) {
            ll in = 0, out = n+1;
            while (out - in > 1) {
                ll m = (in + out) / 2;
                (sq(m) <= sq(mid) - sq(i) ? in : out) = m;
            }
            cnt += in;
            if (cnt >= n) break;
        }
        return cnt;
    };

    ld ok = n+1, ng = 0;
    for (int t = 0; t < 200; ++t) {
        ld mid = (ok + ng) / 2;

        
        (f(mid) >= n ? ok : ng) = mid;
    }
    dbg(f(ok))
    cout << fixed << setprecision(20) << ok << '\n';
}