#include<iostream>
#include <bits/stdc++.h>

# define ld  long double
#define ll long long
#define IO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
using namespace std;
const int N = 1e6 + 5, mod = 998244353, M = 17;

ll solve(ld r) {
    // x^2 + y^2 <= r2
    ll ans = 0;
    for (ll i = 1; i <= r; i++) {
        if (i == 0)continue;

        ll y = sqrtl(r * r - i * i);
        ans += 2 * y;
    }
    return 2 * ans;
}

void doWork() {
    int s;
    cin >> s;
    ld low = 0;
    ld high = 1e5;
    while (high - low > 1e-9) {
        ld mid = (low + high) / 2;
        if (solve(mid) > s) {
            high = mid;
        } else {
            low = mid;
        }
    }
    cout << fixed << setprecision(9) << low;
}

int main() {
    IO
    int t = 1;
    //  cin >> t;
    for (int i = 1; i <= t; i++) {
        doWork();
    }
}