#include<bits/stdc++.h>
using namespace std;

#define int long long

int s;

int chk(double R)
{
    int ret=0;
    for(int i=1;i<=R;i++)
    {
        
        int X=i+1>R?1:ceil(sqrt(R*R-(i+1)*(i+1))+1e-9);
        int Y=floor(sqrt(R*R-i*i));
        ret+=(Y-X+1)*i;
    }
    return ret;
}

signed main()
{
    scanf("%lld",&s);
    double l=0,r=1e5;
    // cout<<chk(2.2360679775)<<endl;
    while((r-l)/max(1.,r)>1e-9)
    {
        double mid=(l+r)/2;
        if(chk(mid)*4>=s)
            r=mid;
        else
            l=mid;
    }
    printf("%.10lf\n",r);
}