#include <bits/stdc++.h>

#define f first
#define s second
#define pb push_back
#define mp make_pair

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;

const int N = 300500, inf = 1e9, mod = 998244353;
const ll INF = 1e18;

int sum(int a, int b) {
    a += b;
    if (a >= mod)
        a -= mod;
    return a;
}

int sub(int a, int b) {
    a -= b;
    if (a < 0)
        a += mod;
    return a;
}

int mult(int a, int b) {
    return 1ll * a * b % mod;
}

int bp(int a, int b) {
    int res = 1;
    while (b) {
        if (b & 1)
            res = mult(res, a);
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

int inv(int x) {
    return bp(x, mod - 2);
}
ll s;
typedef long double ld;
const ld eps = 1e-9;
ll calc(ld F) {
    ll cur = 0;
    for (int p = 1; ; p++) {
//        cout << p << " ? " << endl;
        ld T = F * F - (ld)p * p;
        if (T < eps) break;
        T = sqrtl(T) + 3;
        ll x = T;
        while (x * x + (ll) p * p > F * F) x--;
        cur += x;
    }
    return 4 * cur;
}
void solve() {
    cin >> s;
    ld l = 0;
    ld r = 1e6;
    for (int iter = 0; iter < 60; iter++) {
        ld mid = (l + r) / 2;
        if (calc(mid) > s) r = mid;
        else l = mid;
    }
    cout << fixed << setprecision(12) << (l + r) / 2 << '\n';
}

int main() {
#ifdef DEBUG
    freopen("input.txt", "r", stdin);
#endif
    ios_base::sync_with_stdio(false);
    int t = 1;
//    cin >> t;
    for (int i = 1; i <= t; i++) {
//        cout << "Case #" << i << endl;
        solve();
    }
}