#include <bits/stdc++.h>

#define endl            '\n'
#define pb             push_back
#define fill(x, y)     memset(x, y, sizeof(x))
#define all(x)         (x).begin(), (x).end()
#define debug(x)       { cerr << #x << " = " << x << endl; }
#define IO	       { ios_base::sync_with_stdio(false); cin.tie(0); }
#define read(x)	       freopen(x, "r", stdin)
#define write(x)       freopen(x, "w", stdout)

using namespace std;

typedef long long      ll;
typedef pair<int, int> ii;
typedef vector<int>    vi;

const double inf = 1e18;
const double pi = acos(-1);

ll s;
ll check(double rad) {
    ll count = 0;
    for(ll i=1; i<=rad; i++) {
        double y = sqrt(rad * rad - i * i);
        count += (ll)y;
    }
    return count * 4LL;
}

void solve() {
    //cout << check(2.5) << endl;

    cin >> s;
    double lo = 0, hi = 1e5;

    int cnt = 1000;
    while(cnt--) {
        //cout << lo << " " << hi << endl;
        double m = (lo + hi) / 2;
        if (check(m) > s) hi = m;
        else lo = m;
    }
    cout << lo << endl;
}

int main() {
    IO;
    cout << fixed << setprecision(10);
    solve();
}