#include<bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

#define ll long long
#define endl '\n'
using namespace std;
using namespace __gnu_pbds;

template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 2e5+7, P1 = 31, P2 = 37, mod= 1e9 + 7;

int mul(int a, int b) {
    return (1LL * a * b) % mod;
}

int add(int a, int b) {
    a = (a + mod) % mod;
    b = (b + mod) % mod;
    return (a + b) % mod;
}

int fp(int b, int p) {
    if (b == 1 or p == 0)
        return 1;

    int ret = fp(b, p >> 1);
    ret = mul(ret, ret);

    if (p & 1)
        ret = mul(ret, b);

    return ret;
}

ll modInv(ll n) {
    return fp(n, mod - 2);
}

ll fact[N], inv[N];

void pre() {
    fact[0] = inv[0] = 1;
    for (ll i = 1; i < N; i++)
        fact[i] = (fact[i - 1] * i) % mod, inv[i] = fp(fact[i], mod - 2);
}

ll nCr(ll n, ll r) {
    if ( r > n)
        return 0;
    return ((fact[n] * inv[r]) % mod * inv[n - r]) % mod;
}

ll nPr(ll n, ll r) {
    return ((fact[n] * inv[n - r])) % mod;
}
int s;
long double eps =  1e-8l;
bool can(long double r) {
    ll rm = 0;
    int x = r;
    int y = 1;
    while (x > 0) {
        while (x > 0 && !(1ll * x * x + 1ll * y * y <= r * r +eps))
            --x;
        rm += x;
        ++y;
    }
    return (4 * rm > s);
}
void doWork() {
    cin >> s;
    long double l = 0, r = 2 * sqrtl(s);
    for (int i = 0; i < 300; ++i) {
        long double m = (l + r) / 2;
        if (can(m))
            r = m;
        else 
            l = m;
    }
    cout << fixed << setprecision(12) << l << endl;

}


int main() {
    ios::sync_with_stdio(false);
    cout.tie(nullptr);
    cin.tie(nullptr);
    pre();
//    freopen("bisector.in","r",stdin);
//    freopen("bisector.out","w",stdout);
    int t = 1;
    // cout << primes.size() << endl;
    // cin >> t;
    while (t--) {
        doWork();
    }
    return 0;
}