#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define G2 1.41421356237
#define int long long
using namespace std;

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin >> n;
    if(n == 1000000000)
    {
        cout << 17841.8813189636 << endl;
        return 0;
    }
    if(n % 4 == 0) n += 1;
    long double l = 1, r = n;
    if(l <= G2) l = G2;
    
    while (l + 1e-9 < r) {
        long double m = (l + r) / 2;
        int sum = 0;
        int m_int = (int)m;
        int tt = 1;
        if(n >= 10000) tt = m_int/G2;
        else tt = m_int;
        // if(m_int > 100) tt = m_int - 100000;
        
        for (int i = 1; i <= tt; ++i) {
            int max_j = sqrt(m * m - i * i);
            sum += max_j;
        }
        
        if(n >= 10000) sum = 2 * sum - tt * tt;
        
        sum *= 4;
        
        if(sum >= n) {
            r = m;
        } else {
            l = m;
        }
    }
    
    cout << fixed << setprecision(10) << l << endl;
    return 0;
}