#include<bits/stdc++.h>

#define ll long long
#define pp push_back
#define endl '\n'
#define all(x) x.begin(),x.end()
#define ld long double
#define PI acos(-1)
#define sin(a) sin((a)*PI/180)
#define cos(a) cos((a)*PI/180)
#define ones(x) __builtin_popcountll(x)
//#define int ll

using namespace std;

void Drakon() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef Clion
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

unsigned long long inf = 1e10;
const double eps = 1e-6;
const int MOD = 1000000007, N = 200005, LOG = 25;

ll gcd(ll x, ll y) {
    return y ? gcd(y, x % y) : x;
}

ll lcm(ll a, ll b) {
    return (a * b) / __gcd(a, b);
}

ll mul(const ll &a, const ll &b) {
    return (a % MOD + MOD) * (b % MOD + MOD) % MOD;
}

ll add(const ll &a, const ll &b) {
    return (a + b + 2 * MOD) % MOD;
}

ll pw(ll x, ll y) {
    ll ret = 1;
    while (y > 0) {
        if (y % 2 == 0) {
            x = mul(x, x);
            y = y / 2;
        } else {
            ret = mul(ret, x);
            y = y - 1;
        }
    }
    return ret;
}

ll get(ld r){
    ll ret = 0;
    for (ll i = 0; i <= r; ++i) {
        if(i + 1 <= r){
            ld cur = r * r - i * i;
            ll x = sqrtl(cur);
            if(x)x = x * 2 + 1;
            else x = 1;

            x --;

            if(!i)ret += x;
            else ret += x * 2;
        }
        else{
            if(!i)break;
            ld cur = r * r - i * i;
            ll x = sqrtl(cur);
            if(x)x = x * 2 + 1;
            else x = 1;

            x --;

            ret += x;
        }
    }

    return ret;
}

void solve() {
    int s;
    cin >> s;
    ld l = 1, r = 1e5, ans;
    for (int i = 0; i < 100; ++i) {
        ld mid = (l + r) / 2;
        if(get(mid) > s){
            ans = mid;
            r = mid;
        }
        else{
            l = mid;
        }
    }
    cout << fixed << setprecision(10) << ans;
}

signed main() {
    Drakon();
    int t = 1;
    //cin >> t;
    while (t--) {
        solve();
    }
}