#include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define subnb true
#define Lnb true
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
const ld EPS = 1e-10;
int s;

bool check(ld r) {
//    int fr = r;
    ll res = 0;
    for (int i = 1; i <= r; i++) {
        ld cur = r * r - (ld)i * i;
        if(cur > EPS) {
            ll h = ll(sqrt(cur));
            res += h * 4;
        }
    }
    return res > s;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> s;
    ld l = 0, r = 1e5, mid;
    rep(it, 0, 60) {
        mid = (l + r) / 2;
        if(check(mid)) r = mid;
        else l = mid;
    }
    cout << fixed << setprecision(15) << r << '\n';

}