#define taskname "C"
#include <bits/stdc++.h>
#define ld long double
#define int long long

using namespace std;
const ld lim = sqrt(2.0L) - 1;

inline int cal(ld x)
{
    int le = (x - trunc(x) >= lim ? trunc(x) : trunc(x-1));
    int wi = sqrt(x*x-le*le);
    int la = le - wi;
    int cx = wi, cy = le, ans = 0, cur = 0;
    for (int i=0; i<la; i++)
    {
        while ((cx+cur)*(cx+cur) + cy*cy <= x * x) cur++;
        ans += cur - 1;
        cy--;
    }
    wi <<= 1;
    le <<= 1;
//    cerr<<le<<" "<<wi<<" "<<ans<<"\n";
    return 2 * le * wi - min(le, wi) * min(le, wi) + 4 * ans;
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
//    cout<<cal(17841.8813190);
    for (int i=1; i<=1; i++)
    {
        int s; ld l = 0, r = 1e5;
        cin>>s;
//        s = i;
        for (int i=1; i<=1000; i++)
        {
            ld m = (l+r)/2;
    //        cerr<<m<<" "<<cal(m)<<"\n";
            if (cal(m) > s) r = m;
            else l = m;
        }
//        cout<<i<<" ";
        cout<<fixed<<setprecision(9)<<r<<"\n";
    }
}