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

#define int long long

int s;

double mysqr(double x)
{
    if(x<0)
        return 0;
    return sqrt(x);
}

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