#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<cmath>
#include<climits>
#include<map>
#include<set>
#include<stack>
#include<iomanip>
#include<cmath>
using namespace std;
using ll = long long;
#define int ll


void solve()
{
    int n;
    cin >> n; 
    if (n >= 1 && n <= 3)
    {
        cout << fixed << setprecision(12) << sqrt(2);
        return;
    }
    if (n == 4)
    {
        cout << fixed << setprecision(12) << sqrt(5);
        return;
    }
    int k = 4;
    while (true)
    {
        if (n <= k * k - 4 && n > (k - 2) * (k - 2) - 4)
        {
            break;
        }
        k += 2;
    }
    k /= 2;
    cout << fixed << setprecision(12) << sqrt(k * k + (k - 1) * (k - 1));
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);

    int T = 1;
    //cin >> T;
    while (T--)
    {
        solve();
    }

    return 0;
}