#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);
    wi <<= 1;
    le <<= 1;
    return 2 * le * wi - min(le, wi) * min(le, wi);
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    int s; ld l = 0, r = 4;
    cin>>s;
    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<<fixed<<setprecision(9)<<r;
}